Allow nullable lifecycle and data_retention template values

[dakrone]

These keys allow using an explicit null as the value to "unset" the configuration when merging multiple component templates. As related to the merging tables seen in elastic/elasticsearch#95979 (comment)

Relates also to the discussion in #2049

[dakrone]

I'm not sure how to fix the CI failure, it says: Error: Input required and not supplied: token

[flobernd]

I think the CI workflow is faulty. This expression:

elasticsearch-specification/.github/workflows/validate-pr.yml

Line 18 in 9eff69a

if: github.repository_owner == 'elastic' # this action will fail if executed from a fork

will always be true as github.repository_owner refers to the "target" repository for pull_request triggers.

It should instead check github.event.pull_request.head.repo.owner (if I remember correctly).

[andreidan]

@dakrone this shouldn't be nullable anymore as we now have the enabled field.