feat(router): customize health-check route and add SSL redirect

I pulled #2781 and #2782 into the same PR so they'd be easier to test. This also enabled me to refactor the default route for both the healthcheck endpoint and SSL redirect into the same config block, cleaning up the config and ensuring they apply to everything (i.e. before the controller, builder, store-gateway, or app routes are processed). 

TESTING: add an SSL cert, enable SSL redirects, change the custom health-check endpoint, and ensure nothing is broken
Sorry, I don't have time to fully test a PR in the next days :-(.

I think this configuration should work:
```
# default routes
    server {
        listen 80 default_server;
        {{ $healthEndpoint := or .deis_router_healthEndpoint "/health-check" }}
        location {{ $healthEndpoint }} {
            default_type 'text/plain';
            access_log off;
            return 200;
        }
    }
    {{ $useSSLRedirect := or .deis_router_redirectAllHTTPToHTTPS "false" }}
    {{ if eq $useSSLRedirect "true" }}
    server {
        listen 80;
        location / {
            return 301 https://$http_host$request_uri;
        }
    }
    {{ end }}
```