feat(pipelinecontrol): add OttlTransform field and make NRQL nullable on PipelineCloudRuleEntity

[pranav-new-relic]

Summary

Prepares pkg/pipelinecontrol for the NGEP schema change in ep-next-gen-api PR #1860, which relaxes PipelineCloudRuleEntity.nrql from Nrql! to Nrql and adds a new ottlTransform sibling field to support OTTL-based pipeline cloud rules alongside existing NRQL rules.

Changes

• EntityManagementPipelineCloudRuleEntity.NRQL: nrdb.NRQL → *nrdb.NRQL with omitempty — null responses from NGEP now deserialise to nil instead of silently coercing to empty string
• OttlTransform field added to EntityManagementPipelineCloudRuleEntity with a new EntityManagementPipelineCloudRuleEntityOttlTransform struct (logStatements, eventStatements, metricStatements, traceStatements)
• getEntityQuery and getEntitySearchQuery updated to fetch ottlTransform { ... } in the ... on EntityManagementPipelineCloudRuleEntity inline fragment
• Create/Update input types are intentionally unchanged — they still carry NRQL nrdb.NRQL (non-pointer) for NRQL-based rules; OTTL input support is deferred until the backend ships

Test plan

• go build ./pkg/pipelinecontrol/... passes (verified locally)
• Existing NRQL-based integration tests pass unchanged (NRQL rules always return non-null nrql)
• After ep-next-gen-api PR #1860 merges and NGEP schema is live: end-to-end read of an OTTL rule returns populated OttlTransform and nil NRQL

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.75%. Comparing base (6773d0a) to head (40bbd0c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1474      +/-   ##
==========================================
+ Coverage   32.71%   32.75%   +0.04%     
==========================================
  Files         148      148              
  Lines        6939     6939              
==========================================
+ Hits         2270     2273       +3     
+ Misses       4455     4454       -1     
+ Partials      214      212       -2     

Flag	Coverage Δ
unit	32.75% <ø> (+0.04%)	⬆️

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