Add task to ensure the yaml tests parse

[jasontedor]

We should add a task, that precommit depends on, that ensures that all REST tests parse. This would catch issues where we are muting REST tests. Today we have a test-mute label to quickly get these mutes in via PRs, and that only runs precommit, but precommit wouldn't catch these issues today since it doesn't parse the REST tests.

[elasticmachine]

Pinging @elastic/es-core-infra

[rjernst]

I wonder if we could do this indirectly by changing rest tests to be generated java, so that instead of running parameterized junit, each test file is a generated junit suite. This would also solve the repro line problem in #41380.

[alpar-t]

Closing in favor of #47793

[jakelandis]

We should consider introducing a JSON schema similar to #54252 and validating the tests against the schema. I know the tests are written in YAML, not JSON, but we should be able to easily programmatically convert via Jackson validation. It would catch parsing errors as well as rules that could be defined by the schema. I imagine the validation could re-use the gradle task introduced in #54252