feat/elasticsearch_watermarks

[ebuerki-lf]

No description provided.

[NavidSassan]

points from AI-review:

1. CHANGELOG.md not updated (CONTRIBUTING.md:238). No ## [Unreleased] / ### Added entry for any of the five new variables.
2. Inconsistent regex check between the four asserts (roles/elasticsearch/tasks/main.yml:143-178). Three asserts use the test form ... is
   ansible.builtin.regex("..."), but the fourth (high_max_headroom, line 174) uses the filter form | ansible.builtin.regex_search(...). They
   behave subtly differently (the filter returns the match or None; truthiness happens to work, but it's not the same as a boolean test). Make
   all four use is ansible.builtin.regex(...).
3. Asserts are not in alphabetical order (CONTRIBUTING.md:76). Current order: flood_stage_frozen_max_headroom, flood_stage_max_headroom,
   low_max_headroom, high_max_headroom. Should be: …flood_stage_max_headroom, high_max_headroom, low_max_headroom. The defaults/main.yml and
   README ordering is already alphabetical — match it here too.
4. Stray extra blank line between the low_max_headroom and high_max_headroom asserts (lines 169–170). Tasks inside a block use a single
   blank line; two blank lines are reserved for separating top-level - block:s (CONTRIBUTING.md:128).
5. Missing range validation for the new percentage variable. elasticsearch__cluster_routing_allocation_disk_watermark_flood_stage_frozen is
   documented as Float (0 <= n <= 1), but unlike the existing three watermarks (asserts at lines 104–126), no 0 <= n <= 1 is number check was
   added. Add one in the same style.
6. README example block missing the new variables (roles/elasticsearch/README.md:397-437).
7. Regex case-sensitivity. ^[0-9]+(b|kb|mb|gb|tb|pb)$ rejects perfectly valid Elasticsearch values like 200MB, 1GB. Either add (?i) /
   IGNORECASE semantics, or document in the README that lowercase is required. The linked byte size units doc shows mixed-case values are
   accepted by ES.
8. when: style. The folded > scalar form is unusual in this codebase — most when: clauses are either single-line strings or a list of
   strings (when: ['x is defined', 'x | length > 0']). The example role uses the list form (roles/example/tasks/main.yml:192-193). Switch for
   consistency.
9. quiet: true on asserts (matches the example role pattern at roles/example/tasks/main.yml:54). The pre-existing asserts in this file also
   lack it, so this is a wider inconsistency, but worth fixing now for the new ones at minimum.
10. Redundant is string guard in template. The four template if blocks gate on is defined and is string and (... | length) > 0. The is
    string part is redundant given the variables are documented as Type: String, validated by regex when set, and | length > 0 already trips on
    undefined-vs-empty. Drop is string.
11. Conventional Commits not followed for any of the branch's commits (CONTRIBUTING.md:30-51):

• fix typo in README
• extend validation checks for _max_headroom variables
• add link to elastic api conventions on byte size units
• fix whitespace, quotation for cluster.routing.allocation.disk.watermark.*.max_headroom values
• allow complete set of cluster.routing.allocation.disk.watermark.* to be set through elasticsearch.yml

12. Duplicate flood_stage range assert at roles/elasticsearch/tasks/main.yml:120-134 — the same check exists twice (lines 120-126 and
    128-134, identical). Pre-dates this PR; could be cleaned up while you're touching this file.