Updates proxy paths

[chaptergy]

• Fixes an oversight in Utilise variable for custom locations proxy_pass #1258 which resulted in the path part of a url not being forwarded to the proxy. Fixes Nginx proxy_pass issue caused by upstream variable #1515.
• Uses a variable in proxy_pass directives for proxy hosts as well, to prevent nginx from crashing if the upstream url is not available. Fixes convert docker name to variable  #927

[jc21]

This is an automated message from CI:

Docker Image for build 1 is available on DockerHub as jc21/nginx-proxy-manager:github-pr-1519

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