Support for upstream TLS in mimir-distributed Helm chart

[mac133k]

Is your feature request related to a problem? Please describe.

Currently Nginx config for the gateway component is rendered from gateway.nginx.config.file variable which has hardcoded http prefixes in all proxy pass directives. This makes the Mimir cluster inaccessible when TLS is enabled for other components.

Describe the solution you'd like

Loki Helm chart has gateway.nginxConfig.schema parameter where URL prefix can be set to https when needed - something like that could be introduced to Mimir's chart.

Describe alternatives you've considered

I set gateway.nginx.config.file in my values overrides with all URLs rewritten with https:// prefixes.

[mac133k]

My chart version is:

NAME                                	CHART VERSION	APP VERSION	DESCRIPTION                                       
grafana/mimir-distributed           	5.4.1        	2.13.0     	Grafana Mimir