chore(Unit Testing): Adds Unit Testing & New Local Development Environment

[timnolte]

All Submissions:

• Have you followed the plugin Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

• Refactors and adds unit tests.
• Fixes Gruntfile testing.
• Adds unit testing w/ Docker using the Dev Container image.
• Updates NPM & Composer dependencies.

How to test the changes in this Pull Request:

1. Use either GitHub Codespaces or local Visual Studio Code. (see: https://github.com/forumone/wp-cfm/wiki/How-to-setup-the-plugin-development-environment)
2. Confirm that the development environment starts up.
3. Run composer phpunit to confirm running tests. (Also observe GitHub Actions)

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

[github-actions]

Coverage report for commit: 2a55e47
File: clover.xml

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      └─────────────────────────┘
 *Legend:* █ = Current Distribution 

Summary - Lines: 0.93% | Methods: 1.01%

Files	Lines	Methods	Branches
/workspaces/openid-connect-generic/includes
functions.php	-	100.00%	100.00%
openid-connect-generic-client-wrapper.php	-	-	100.00%
openid-connect-generic-client.php	-	-	100.00%
openid-connect-generic-login-form.php	-	-	100.00%
openid-connect-generic-option-logger.php	-	-	100.00%
openid-connect-generic-option-settings.php	47.37%	12.50%	100.00%
openid-connect-generic-settings-page.php	-	-	100.00%
/workspaces/openid-connect-generic
openid-connect-generic.php	1.77%	-	100.00%

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