Sign ansi2json state by default

What does this MR do and why?

Sign ansi2json state by default

This enables the flag sign_and_verify_ansi2json_state by default. The flag should in principle also be safe to remove, but that's a slightly bigger code change that has a greater chance of back-and-forth with reviewers. I have an upcoming holiday and want to make sure this change makes it into 16.0 in some form so we can close out the associated issue.

See #404718 (closed)

How to set up and validate

You can verify that the feature is already enabled on GitLab.com using ChatOps:

/chatops run feature get sign_and_verify_ansi2json_state

It has been like that for over a week, see the rollout issue.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.