Performance improvements (1/3) to example-advanced.nginx.conf - #1709

This is the first of three projected PRs meant to close #1704. The patch is separated out to make testing easier. The second and third parts will cover security headers and load balancing (between workers/cores) respectively.

This patch consists of standard optimisations to nginx configuration and regex:

1. Using return instead of rewrite to avoid interpreting ^(.*)$ and creating additional variable. https://blog.nginx.org/blog/creating-nginx-rewrite-rules
2. Using non-capturing groups where nothing needs to be saved to variables.
3. Simplifying \/ to / as nginx doesn’t use forward slash as regex delimiter. https://www.f5.com/company/blog/nginx/regular-expression-tester-nginx
4. Removing redundant .*$ as .* and $ cancel each other out.
5. Using exact (=) or prefix (^~) match instead of regex match whenever it’s possible to preserve the same semantics, as both terminate the search immediately on match before any regex gets searched.