Drop the unused "mongo" log source from the queue populator

[delthas]

The "mongo" log source made the queue populator tail MongoDB's internal replica-set oplog (local.oplog.rs) through arsenal's mongoclient.LogConsumer. It is broken on MongoDB >= 7.1 (the oplog h field used as a cursor was removed — ARSN-545, closed Won't Fix) and unused by every deployment: Federation sets bucketd, and zenko-operator overrides its mongo fallback to kafka whenever the oplog populator is enabled (the default on all mongo-backed deployments).

Changes:

• Delete MongoLogReader and its case 'mongo' in QueuePopulator._setupLogSources(), plus related jsdoc and the log-source error message.
• Remove 'mongo' from the logSource joi enum.
• Remove the mongo-specific opaque-string offset handling in LogReader._readLogOffset() — stored offsets are numeric for all remaining log sources.
• Switch the sample config and unit-test fixtures from logSource: "mongo" to "kafka".

The queuePopulator.mongo config section is intentionally kept: it is the shared MongoDB connection configuration used by the lifecycle bucket processor, notification queue processor, mongo processor and oplog populator.

Follow-ups tracked separately: removing mongoclient/LogConsumer + ListRecordStream from arsenal, and (optionally) the logSource: "mongo" fallback in zenko-operator.

Issue: BB-836

[bert-e]

Hello delthas,

My role is to assist you with the merge of this
pull request. Please type @bert-e help to get information
on this process, or consult the user documentation.

Available options

name	description	privileged	authored
/after_pull_request	Wait for the given pull request id to be merged before continuing with the current one.
/bypass_author_approval	Bypass the pull request author's approval	⭐
/bypass_build_status	Bypass the build and test status	⭐
/bypass_commit_size	Bypass the check on the size of the changeset TBA	⭐
/bypass_incompatible_branch	Bypass the check on the source branch prefix	⭐
/bypass_jira_check	Bypass the Jira issue check	⭐
/bypass_peer_approval	Bypass the pull request peers' approval	⭐
/bypass_leader_approval	Bypass the pull request leaders' approval	⭐
/approve	Instruct Bert-E that the author has approved the pull request.		✍️
/create_pull_requests	Allow the creation of integration pull requests.
/create_integration_branches	Allow the creation of integration branches.
/no_octopus	Prevent Wall-E from doing any octopus merge and use multiple consecutive merge instead
/unanimity	Change review acceptance criteria from one reviewer at least to all reviewers
/wait	Instruct Bert-E not to run until further notice.

Available commands

name	description	privileged
/help	Print Bert-E's manual in the pull request.
/status	Print Bert-E's current status in the pull request.
/clear	Remove all comments from Bert-E from the history TBA
/retry	Re-start a fresh build TBA
/build	Re-start a fresh build TBA
/force_reset	Delete integration branches & pull requests, and restart merge process from the beginning.
/reset	Try to remove integration branches unless there are commits on them which do not appear on the source branch.

Status report is not available.

[codecov]

Codecov Report

❌ Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.70%. Comparing base (1d77181) to head (ddbe22a).

Files with missing lines	Patch %	Lines
lib/queuePopulator/LogReader.js	60.00%	2 Missing ⚠️
lib/queuePopulator/QueuePopulator.js	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
lib/config.joi.js	100.00% <100.00%> (ø)
lib/queuePopulator/IngestionPopulator.js	67.11% <ø> (ø)
lib/queuePopulator/QueuePopulator.js	82.74% <0.00%> (+0.64%)	⬆️
lib/queuePopulator/LogReader.js	83.33% <60.00%> (+10.91%)	⬆️

... and 1 file with indirect coverage changes

Components	Coverage Δ
Bucket Notification	80.27% <ø> (ø)
Core Library	81.90% <57.14%> (+0.68%)	⬆️
Ingestion	70.13% <ø> (ø)
Lifecycle	80.25% <ø> (ø)
Oplog Populator	85.83% <ø> (ø)
Replication	61.98% <ø> (ø)
Bucket Scanner	85.76% <ø> (ø)

@@                 Coverage Diff                 @@
##           development/9.5    #2795      +/-   ##
===================================================
+ Coverage            75.43%   75.70%   +0.27%     
===================================================
  Files                  201      200       -1     
  Lines                13935    13913      -22     
===================================================
+ Hits                 10512    10533      +21     
+ Misses                3413     3370      -43     
  Partials                10       10              

Flag	Coverage Δ
api:retry	9.06% <14.28%> (+0.01%)	⬆️
api:routes	8.84% <14.28%> (+0.01%)	⬆️
bucket-scanner	85.76% <ø> (ø)
ft_test:queuepopulator	10.36% <14.28%> (+1.22%)	⬆️
ingestion	12.23% <57.14%> (-0.03%)	⬇️
lib	8.79% <14.28%> (+0.01%)	⬆️
lifecycle	19.28% <14.28%> (+0.03%)	⬆️
notification	1.02% <0.00%> (+<0.01%)	⬆️
oplogPopulator	0.13% <0.00%> (+<0.01%)	⬆️
replication	18.83% <14.28%> (+0.03%)	⬆️
unit	54.71% <14.28%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[bert-e]

Waiting for approval

The following approvals are needed before I can proceed with the merge:

• the author

• 2 peers