Update Branch Rules query to return merge options
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Currently merge options can be queried from a project like:
```
query mergeOptions{
project(fullPath:"root/test-project") {
id
updateDiffDiscussionPositions
removeSourceBranchAfterMerge
}
}
```
We should expose the attributes from the models created in https://gitlab.com/gitlab-org/gitlab/-/issues/504648 the branch rule type.
i.e We should be able to perform queries like
```
query getBranchRules{
project(fullPath:"root/test-project") {
id
branchRules {
nodes {
id
name
updateDiffDiscussionPositions
removeSourceBranchAfterMerge
}
}
}
}
```
For AllBranchesRules these should be project level settings. For other branch rules, these should be the branch specific settings.
issue