SE-1496 conditionally re-enable user change password form in admin

Description

This PR enables setting/changing a user's password from the django admin, gated
behind a waffle switch.

This behaviour was disabled across https://github.com/edx/edx-platform/pull/18970
and https://github.com/edx/edx-platform/pull/18972.

*JIRA tickets*:

*Dependencies*: None

*Sandbox URL*: TBD - sandbox is being provisioned.

*Merge deadline*: None

*Testing instructions*:

1. login to the admin on the *lms* as a superuser
2. navigate the admin change page for a user (eg `/admin/auth/user/1/change/`)
3. verify that there is no link to a password change form in the description
for the password field. (You should not see " but you can change the
password using this form.")
4. change the current url from .../change/ to .../password/ (eg.
`/admin/auth/user/1/password/`)
5. verify that a 404 page is displayed
6. repeat steps 2 - 5 on the *cms*
7. navigate to the waffle switch admin page (`/admin/waffle/switch`) - doesn't
matter if cms or lms admin.
8. add a new waffle switch named `common.changeuserpassword_admin` and enable
it.
9. restart the cms and lms apps (reboot the server or run
`/edx/bin/supervisorctl restart lms: cms:` from a shell).
10. log in to the admin on the *lms* as a superuser
11. navigate the admin change page for a user (eg `/admin/auth/user/1/change/`)
12. verify that a link to a password change form ("but you can change the
password using this form") is visible.
13. click the form link and verify that the page loads correctly and the user
password can be changed
14. repeat the previous 4 steps from the *cms* admin.

*Author notes and concerns*:

1. A waffle switch may not be the best approach, because changes aren't fully
applied until the server is restarted. An option under settings might be
more appropriate, as then it will not be possible for the behaviour to be
partially toggled.

*Reviewers*

  • [ ] @pomegranited

  • [ ] edX reviewer[s] TBD

*Settings*
```yaml
```

Status

Assignee

Marco Morales

Reporter

Open Source Pull Request Bot

Labels

Contributor Name

Samuel Walladge

Repo

edx/edx-platform

Customer

Epic Link

None

OSCM Assignee

None

Priority

Unset
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