Fix CORS does not work when used with Basic Auth

[ms140569]

This PR fixes #336 when CORS is used together with Basic Auth.

The Authorization header is now added to the cors-allow-headers list to work with the Basic Auth.
Also, the server will allow OPTIONS requests without an Authorization header since it is not required according to the spec.

Test cases will follow in a separate PR.

[semanticdiff-com]

Review changes with SemanticDiff.

Analyzed 3 of 4 files.

Overall, the semantic diff is 23% smaller than the GitHub diff.

	Filename	Status
❔	docs/content/features/cors.md	Unsupported file format
✔️	src/cors.rs	23.1% smaller
✔️	src/handler.rs	4.17% smaller
✔️	src/settings/cli.rs	Analyzed

[joseluisq]

For now, the PR has what we need to fix the issue.
In addition, I made some minor improvements to the src/cors.rs as well as added/updated a few log entries and updated the CORS page mentioning the new allowed authorization header.

However, as discussed. It would be great to add the necessary tests for the features used together. So feel free to add them here or let me know if you want to do it in a separate PR.

[joseluisq]

Just please update the PR description and title accordingly. Also, link the issue that you are fixing.

[joseluisq]

Thanks!