Add ability to generate a new migration token

[joshcanhelp]

Changes

Adds a button to generate a new migration token for user migration setups.

References

• Fixes User Migration set as PHP constant causes token to not be generated #620
• Pending Docs PR commit

Testing

Failed tests for new field and functionality

Manual Steps:

1. Paste the following in wp-config.php:

define( 'AUTH0_ENV_MIGRATION_WS',  true );
define( 'AUTH0_ENV_MIGRATION_TOKEN', 'THIS_IS_MY_MIGRATION_TOKEN' );

2. Refresh the plugin settings page and see the constant-based settings:

3. Save the settings page
4. Comment out the AUTH0_ENV_MIGRATION_TOKEN definition added above
5. Refresh the settings page to see an empty migration token:

6. Click the Generate New Migration Token button
7. See the alert message:

8. Click Ok
9. See "Save or refresh this page to see changes." in the migration token box:

9. Refresh the page and see a token value

• I included manual testing steps above, if applicable
• This change adds unit test coverage
• This change has been tested on WP 5.1.1

Checklist

• All existing and new tests complete without errors
• All code quality tools/guidelines in the Contribution guide have been run/followed
• All active GitHub CI checks have passed

[codecov-io]

Codecov Report

Merging #640 into master will increase coverage by 0.69%.
The diff coverage is 77.77%.

@@             Coverage Diff              @@
##             master     #640      +/-   ##
============================================
+ Coverage     40.02%   40.72%   +0.69%     
- Complexity     1235     1239       +4     
============================================
  Files            51       51              
  Lines          3765     3784      +19     
============================================
+ Hits           1507     1541      +34     
+ Misses         2258     2243      -15

Impacted Files	Coverage Δ	Complexity Δ
lib/admin/WP_Auth0_Admin.php	0% <0%> (ø)	17 <0> (ø)	⬇️
lib/admin/WP_Auth0_Admin_Basic.php	20.94% <0%> (ø)	28 <0> (ø)	⬇️
lib/admin/WP_Auth0_Admin_Advanced.php	46.17% <95.45%> (+9.2%)	67 <2> (+4)	⬆️

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[damieng]

It's kind of odd for buttons to disappear on UIs. Is there a problem with leaving it there in case something went wrong? Or do they really need to refresh the page?

[joshcanhelp]

The function is success-only and doesn't need any data, just a 200 code. Putting the new token in the code block would be nice but would require sending the new token unnecessarily. I can't refresh the page for the user in case there are other changes that have not been saved.