Plugins: Introduce Plugin Registry (#47200)

* introduce registry write/read separation

* internal + external registries

* fix tests

* fixup

* rename

* move interfaces

* back to plugins.Store

* fix registry name

* remove context.TODOs

* remove some ctx for now

* tidy

* remove dupe logic

* update naming

* move from manager.go to store

* amend logger name

* new store writer svc

* restrict changes

* more simplifying

* move interfaces around

* remove unused

* fix linter

* tidy

* add registry test

* fix tests

* revert testdata changes

* revert testdata changes #1

* revert testdata changes #2

* revert testdata changes #3

* revert testdata changes #4

* revert testdata changes #5

* revert testdata changes

* fixup testdata

* remove unused log

* update naming in test

* adjust ctx in test

pkg/plugins/manager/loader/ifaces.go

@@ -0,0 +1,13 @@
+package loader
+
+import (
+	"context"
+
+	"github.com/grafana/grafana/pkg/plugins"
+)
+
+// Service is responsible for loading plugins from the file system.
+type Service interface {
+	// Load will return a list of plugins found in the provided file system paths.
+	Load(ctx context.Context, class plugins.Class, paths []string, ignore map[string]struct{}) ([]*plugins.Plugin, error)
+}