add field_serializer to computed_field

[andresliszt]

This PR tries to add field_seralizer into computed fields described in #6964

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @hramezani

[andresliszt]

Updating unit tests

[andresliszt]

please review

[adriangb]

This looks good @andresliszt ! Can you add a test using Annotated[..., PlainSerializer()] as the return type from a computed field function?

[andresliszt]

This looks good @andresliszt ! Can you add a test using Annotated[..., PlainSerializer()] as the return type from a computed field function?

done!, is that what you wanted? Thanks for the observation