Provide a mechanism to register callbacks for branch merge approval

[jeremystretch]

Plugin Version

v0.5.2

Proposed functionality

Introduce a mechanism that other plugins can use to prevent the merging of a branch, e.g. to enforce a change policy. This could be a class method on the Branch model used to register callback functions, which return a boolean (pass or fail) and optionally a failure reason. For example:

import datetime
from netbox_branching.models import Branch

def check_if_friday(branch):
    if datetime.date.today().weekday() == 4:
        return False, "No merging on Friday!"

Branch.register_merge_check(check_if_friday)

This will complement (or, potentially, replace) the current ability to manually register such functions via the plugin's configuration:

PLUGINS_CONFIG = {
    'netbox_branching': {
        'merge_validators': ['myplugin.check_if_friday'],
    }
}

Use case

This will enable other plugins to integrate with the branch merging functionality and enforce administrative policy.

External dependencies

N/A