Adds feature to Edit Custom certificates.

[rumansaleem]

Closes #1618 & #1911

• Adds a PUT API to update certificate data (using only nice_name for now). The method to call this API already existed in client-side.
• Updates the existing Form UI & Logic:
  • Conditionally calls updating or creating a certificate.
  • Makes certificates non-required in case of editing
  • Existing API call to upload files to existing certificate, replaces the existing files, in case files already exists.

Screenshots

Edit Menu (only for custom certificates)

Edit Form (re-uses existing form)

[nginxproxymanagerci]

Docker Image for build 2 is available on
DockerHub
as nginxproxymanager/nginx-proxy-manager-dev:pr-4425

Note: ensure you backup your NPM instance before testing this image! Especially if there are database changes
Note: this is a different docker image namespace than the official image

[rumansaleem]

Hey @jc21 can you please review this PR?