Hide `delete branch` button for branches protected by a security policy

Why are we doing this work

• when a protected branch is affected by a security policy with the setting block_branch_modification: true, it cannot be deleted
• users may be confused at the Delete button still being displayed

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

• frontend hide delete button

Verification steps