feat(actions): added YAML linting action using yamlfmt, and linted existing YAML files

[tombch]

This PR adds an action yamlfmt-lint which checks for correctly formatted YAML, for all YAML files excluding the helm templates and Github actions.

The linting is done using yamlfmt, and a couple of settings have been added in the .yamlfmt.yml:

• trim_trailing_whitespace: true: trims trailing whitespace, and was required to preserve multiline script/run tags in GitHub actions (mentioned here: Multiline syntax with pipe (|) not retained google/yamlfmt#185).
• retain_line_breaks_single: true: any instance of multiple line breaks is squashed down into a single line break.

Any suggestions for this are very welcome! Some caveats I have noticed with the formatting is that it does not preserve any indenting/aligning within comments (mentioned here: google/yamlfmt#290)

For the Github actions, it forces any run/script tags to use |- rather than |. Possibly the workflows shouldn't be included in linting? (Github actions are now excluded from linting)

PR Checklist

• All necessary documentation has been adapted.
• The implemented feature is covered by appropriate, automated tests.
• Any manual testing that has been done is documented (i.e. what exactly was tested?)

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[anna-parker]

Hi @tombch this is amazing! if the github actions are hard to do you can start with excluding them and we can add them in a later PR - thanks for finding this and working on it!

[claude]

Claude finished @tombch's task in 2m 9s —— View job

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Code Review

• Gather context and read changed files
• Review workflow file
• Review yamlfmt config
• Review pre-commit config changes
• Review reformatted YAML files
• Post final review

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Overall this is a clean, well-scoped addition. The yamlfmt CI action works correctly (the yamlfmt-lint check passes ✅), and the exclusions for .github workflows and helm templates are the right call given the caveats mentioned in the PR description.

Two things worth addressing:

1. Pin the container image version — ghcr.io/google/yamlfmt:latest in the workflow can cause non-deterministic failures if a new release changes formatting rules. Pinning to a tag (e.g. v0.16.0) keeps the CI reproducible. See inline comment.

2. No local pre-commit hook — The changes to .pre-commit-config.yaml are just the existing hooks being reformatted by yamlfmt itself. A yamlfmt pre-commit hook isn't actually added, so developers won't get YAML linting when committing locally. See inline comment for a suggested addition.

The YAML formatting changes themselves look correct — the indentation fixes in the references lists in values.yaml are actually semantically meaningful (the list items were previously under-indented relative to their parent key), and the trailing whitespace cleanup is purely cosmetic.

[anna-parker]

lgtm! I would maybe pin to a specific ymlfmt version as suggested to not have main tests potentially go red as soon as there is a new release :-)