Add Basic Auth authentication

[DL6ER]

What does this implement/fix?

Add ability to create a session using HTTP Basic Auth (RFC 7617).

Example:

$ curl -s 127.0.0.1/api/auth | jq .session.valid
false

$ curl -s -u pi-hole:ABC 127.0.0.1/api/auth | jq .session.valid
true

Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/http-basic-authorization-header-support/65956/5

[DL6ER]

I don't think this is the way we should go for the reasons pointed out in the related Discourse discussion (see link above). I will close this but still leave the branch alive for some time in the unlikely case there are striving arguments to recover this.