Expose require_sha_for_merge on group settings API

What does this MR do and why?

This MR exposed the require_sha_for_merge and lock_require_sha_for_merge values on the GET group endpoint api/v4/groups/id and allows for their modification via the PUT on the endpoint.

References

Main epic: https://gitlab.com/groups/gitlab-org/-/work_items/20551+

Screenshots or screen recordings

Before	After

How to set up and validate locally

curl --location 'http://gdk.test:3000/api/v4/groups/:id' \
--header 'PRIVATE-TOKEN: glpat-YOURTOKEN' 

# `require_sha_for_merge` and `lock_require_sha_for_merge` should be in the payload

curl --location --request PUT 'http://gdk.test:3000/api/v4/groups/:id' \
--header 'PRIVATE-TOKEN: glpat-YOURTOKEN' \
--header 'Content-Type: application/json' \
--data '{
    "require_sha_for_merge": true,
    "lock_require_sha_for_merge": false
}'

# `require_sha_for_merge` and `lock_require_sha_for_merge` should be updated as specified

MR acceptance checklist

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