Support unix socket to collect NGINX OSS and Plus metrics

[aphralG]

Proposed changes

• Changed nginxConfigContext.PlusAPI & nginxConfigContext.StubStatus from strings to APIDetails which is a struct containing URL and Location & Listen to support unix sockets. Where listen is the socket if using sockets, same change was made to OSS & Plus Receivers Config & Otel template, example below
• Changed Stub Status Scraper to use default http client instead of otel http client to enable the setting of the dial context for sockets to work.
• Removed duplicate code in config parser, the same functions are used to get StubStatus & PlusAPI
  • urlsForLocationDirectiveAPIDetails replaces urlsForLocationDirective
  • pingAPIEndpoint replaces pingPlusAPIEndpoint & pingStubStatusAPIEndpoint
  • crossplaneConfigTraverseAPIDetails replaces crossplaneConfigTraverseStr
  • apiCallback replaces plusAPICallback & stubStatusAPICallback
  • traverseAPIDetails replaces traverseStr
  • The format for the unix api and stub status format were taken from other projects to be consistent

&APIDetails{
			URL:      "[http://localhost:80/status](http://localhost/status)",
			Listen: "localhost:80",
                         Location: "/status"
		},

&APIDetails{
			URL:      ""http://config-status/stub_status",
			Listen: "unix:/var/run/nginx/nginx-status.sock",
                         Location: "/stub_status"
		},

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[dhurley]

Can you update the README files for the 2 receivers as well?