Bug 22174: Add link to help page for API key management

Bug 22174: Add link to help page for API key management

Makes the help link on the API key management page point
to the proper section in the Koha manual.

To test:
- Activate RESTOAuth2ClientCredentials system preference
- Go to any patron account
- Go to More > Manage API keys
- Click on the Help link in top right corner
- Verify that the right section of the Koha manual displays

Signed-off-by: Hayley Mapley <hayleymapley@catalyst.net.nz>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>