[api] pull request field Mergeable = ture but not aproved

[6543]

either add a check to IsMerged witch check branch protection or add an extra field witch show if a pull is realy ready to merge (required ci passed & required reviews)

gitea version: v1.13.0

[noerw]

I think restricting the current IsMergeable field is much easier to understand for API consumers

[bilderbuchi]

I think this should be a separate field, and the "mergeable" field should remain scoped on the Git-mergeability.
Otherwise, e.g. CI services will have a hard time judging when to start a CI run on a PR update -- right now it gets held off if there is a merge conflict (i.e. mergeable is false).
If protection rule results etc. would get folded into the same flag, CI would not run as long as e.g. there are not enough reviews, which will probably not come as long as CI has not run, ...