Update branchRuleUpdate mutation to allow editing of all protected branch attributes

Part of Implement the ability to add branch Protections (&12524 - closed)

The branchRuleEdit mutation should accept all attributes for branchProtection that a protected branch can have, i.e. mergeAccessLevels, pushAccessLevels, allowForcePush, requireCodeOwnerApproval. We also have unprotectAccessLevels but it looks like we won't allow users to set these in the UI for now.

These attributes are only possible to set on Projects::BranchRule objects and not Projects::AllBranchesRule and Projects::AllProtectedBranchesRule objects, we might need some validation in the mutation to handle misuse.