Extend ProtectDefaultBranchService to support security policy project

What does this MR do?

Addresses #335661 (closed) and based on !65830 (comment 630697095)

As a part of &5362 (closed), a GraphQL mutation was introduced to create security policy project for a given project. The newly created project should have the default branch protected and it should override the default branch protection configured for the group and only maintainers should have access to merge and no one having access to push to the default branch. But there was a bug in creating protected branch. The bug due to race-condition in creating protected branch for security policy project was because there were 2 independent write paths. But the fix to the race-condition as implemented in !65830 (closed) had performance problems because of transaction.

This MR checks if the project is a security policy project when the protected branch rule is created for default branch. For security policy project, the merge and push access levels are set to MAINTAINER and NO_ACCESS respectively. This removes the need to create another protected branch in Security::SecurityOrchestrationPolicies::ProjectCreateService

!66448 (merged) removes the part that creates protected branch in Security::SecurityOrchestrationPolicies::ProjectCreateService

Screenshots or Screencasts (strongly suggested)

Does this MR meet the acceptance criteria?

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• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

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• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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