feat: Add django admin cmd for adding explicit plugin access

[tiina303]

Problem

Want to switch over to using explicit access instead of if org has any plugins that are enabled.
Follow-up to #21680

Thought about adding a UI for this and realised it's only us + support engineers maybe using it and that's too much work for that.

Changes

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Does this work well for both Cloud and self-hosted?

How did you test this code?

Ran locally

DEBUG=1 python manage.py change_plugin_private_access --organization-id 018e628e-99d7-0000-ff0b-1c5490bdc38f --plugin-id 5 --live-run
2024-05-08 02:29:41 [warning  ] ['️Environment variable DEBUG is set - PostHog is running in DEVELOPMENT MODE!', 'Be sure to unset DEBUG if this is supposed to be a PRODUCTION ENVIRONMENT!']
/Users/tiina/posthog/posthog2/env/lib/python3.10/site-packages/dlt/common/configuration/specs/base_configuration.py:155: UserWarning: Missing default value for field subdomain on ZendeskCredentialsBase. None assumed. All fields in configspec must have default.
  warnings.warn(
2024-05-08T00:29:45.029100Z [warning  ] Skipping async migrations setup. This is unsafe in production! [posthog.apps] pid=2782 tid=4298851712
2024-05-08T00:29:45.032737Z [info     ] AXES: BEGIN LOG                [axes.apps] pid=2782 tid=4298851712
2024-05-08T00:29:45.033819Z [info     ] AXES: Using django-axes version 5.9.0 [axes.apps] pid=2782 tid=4298851712
2024-05-08T00:29:45.033872Z [info     ] AXES: blocking by IP only.     [axes.apps] pid=2782 tid=4298851712
2024-05-08T00:29:45.458294Z [info     ] Plugin Language URL stripper is currently explicitly allowed for organizations: [] [posthog.management.commands.change_plugin_private_access] pid=2782 tid=4298851712
2024-05-08T00:29:45.461122Z [info     ] Organization host currently has explicit access to plugins: [Taxonomy Plugin] [posthog.management.commands.change_plugin_private_access] pid=2782 tid=4298851712
2024-05-08T00:29:45.461201Z [info     ] Target organization 018e628e-99d7-0000-ff0b-1c5490bdc38f is named host currently does not have access [posthog.management.commands.change_plugin_private_access] pid=2782 tid=4298851712
2024-05-08T00:29:45.466706Z [info     ] Added access                   [posthog.management.commands.change_plugin_private_access] pid=2782 tid=4298851712
(env)