feat(api): feature flags (#7356)

* feat(api): feature API proto definitions

* update proto based on discussion with @livio-a

* cleanup old feature flag stuff

* authz instance queries

* align defaults

* projection definitions

* define commands and event reducers

* implement system and instance setter APIs

* api getter implementation

* unit test repository package

* command unit tests

* unit test Get queries

* grpc converter unit tests

* migrate the V1 features

* migrate oidc to dynamic features

* projection unit test

* fix instance by host

* fix instance by id data type in sql

* fix linting errors

* add system projection test

* fix behavior inversion

* resolve proto file comments

* rename SystemDefaultLoginInstanceEventType to SystemLoginDefaultOrgEventType so it's consistent with the instance level event

* use write models and conditional set events

* system features integration tests

* instance features integration tests

* error on empty request

* documentation entry

* typo in feature.proto

* fix start unit tests

* solve linting error on key case switch

* remove system defaults after discussion with @eliobischof

* fix system feature projection

* resolve comments in defaults.yaml

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/feature/feature_test.go

@@ -0,0 +1,43 @@
+package feature
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestKey(t *testing.T) {
+	tests := []string{
+		"unspecified",
+		"login_default_org",
+		"trigger_introspection_projections",
+		"legacy_introspection",
+	}
+	for _, want := range tests {
+		t.Run(want, func(t *testing.T) {
+			feature, err := KeyString(want)
+			require.NoError(t, err)
+			assert.Equal(t, want, feature.String())
+		})
+	}
+}
+
+func TestLevel(t *testing.T) {
+	tests := []string{
+		"unspecified",
+		"system",
+		"instance",
+		"org",
+		"project",
+		"app",
+		"user",
+	}
+	for _, want := range tests {
+		t.Run(want, func(t *testing.T) {
+			level, err := LevelString(want)
+			require.NoError(t, err)
+			assert.Equal(t, want, level.String())
+		})
+	}
+}