Fixes certificate renewal

[chaptergy]

This will fix the certificate renewal in some cases:

• Automatic renewal using DNS challenges used to always fail due to the authenticator being overwritten globally
• Automatic renewal using the HTTP challenge used to fail if the domain was not used in any host.

This PR removes the global authenticator being set, since it is always set certificate specific as well, and adds the letsencrypt challenge functionality to the default host (using any of the congratulations site, 404 page, redirect or custom page)

Should fix #1282, probably fixes #1220, fixes #1031, should fix #1018 and fixes #860

[chaptergy]

The failing check does not seem related to the content of the PR.

[jc21]

This is an automated message from CI:

Docker Image for build 1 is available on DockerHub as jc21/nginx-proxy-manager:github-pr-1286

Note: ensure you backup your NPM instance before testing this PR image! Especially if this PR contains database changes.

[jc21]

This is an automated message from CI:

Docker Image for build 2 is available on DockerHub as jc21/nginx-proxy-manager:github-pr-1286

Note: ensure you backup your NPM instance before testing this PR image! Especially if this PR contains database changes.

[jc21]

This is an automated message from CI:

Docker Image for build 3 is available on DockerHub as jc21/nginx-proxy-manager:github-pr-1286

Note: ensure you backup your NPM instance before testing this PR image! Especially if this PR contains database changes.