Add `id_tokens` field to `ci_builds_metadata`

What does this MR do and why?

This MR adds an id_tokens JSONB field to the ci_builds_metadata table. This field will be used to store JWT configurations for CI jobs. It is the first MR for #356986 (closed).

Note: the id_tokens field is closely related to the secrets field, and the code in this MR closely matches the secrets code and tests.

Screenshots or screen recordings

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