Dashboard: Mix initials and custom gravatars in recent viewers list (#47212)

* Use Wiring to initialize Avatar Cache Server

Create AvatarCacheServer Provider function and pass it in as an
argument to HTTPServer. Also convert CacheServer to a singleton
so that we keep all cached Avatar info in one place for easier access

* Refactor avatar cache server and add 'isCustom' check

Avatar cache server needs to perform two similar fetches
back-to-back; break up functions to allow for easy reuse.
Then add handling to see if a user has a custom avatar.

* Add additional accessors so that /recents api can easily use the cache

* Minor mods to avatar server to facilitiate unit testing

* add unit tests for avatar fetching

* add error handling in case we somehow fetch gravatars while they are disabled

* linting: read error return value in unit test

* Use http package status codes

Co-authored-by: Ezequiel Victorero <evictorero@gmail.com>

* Use http package status codes

Co-authored-by: Ezequiel Victorero <evictorero@gmail.com>

* Use http package status codes

Co-authored-by: Ezequiel Victorero <evictorero@gmail.com>

* Incorporate suggestions from PR
-avoid mutating arguments
-change error handler function to private and make name more descriptive

Co-authored-by: Ezequiel Victorero <evictorero@gmail.com>

pkg/api/api.go

@@ -4,7 +4,6 @@ package api
 import (
 	"time"
 
-	"github.com/grafana/grafana/pkg/api/avatar"
 	"github.com/grafana/grafana/pkg/api/frontendlogging"
 	"github.com/grafana/grafana/pkg/api/routing"
 	"github.com/grafana/grafana/pkg/infra/log"
@@ -542,8 +541,7 @@ func (hs *HTTPServer) registerRoutes() {
 	r.Any("/api/gnet/*", reqSignedIn, hs.ProxyGnetRequest)
 
 	// Gravatar service.
-	avatarCacheServer := avatar.NewCacheServer(hs.Cfg)
-	r.Get("/avatar/:hash", avatarCacheServer.Handler)
+	r.Get("/avatar/:hash", hs.AvatarCacheServer.Handler)
 
 	// Snapshots
 	r.Post("/api/snapshots/", reqSnapshotPublicModeOrSignedIn, hs.CreateDashboardSnapshot)