feat: use appearance.Fetcher in agentapi (#11770)

This PR updates the Agent API to use the appearance.Fetcher, which is set by entitlement code in Enterprise coderd.

This brings the agentapi into compliance with the Enterprise feature.

coderd/agentapi/servicebanner.go

@@ -2,37 +2,22 @@ package agentapi
 
 import (
 	"context"
-	"database/sql"
-	"encoding/json"
+	"sync/atomic"
 
 	"golang.org/x/xerrors"
 
-	agentproto "github.com/coder/coder/v2/agent/proto"
-	"github.com/coder/coder/v2/coderd/database"
-	"github.com/coder/coder/v2/codersdk"
+	"github.com/coder/coder/v2/agent/proto"
+	"github.com/coder/coder/v2/coderd/appearance"
 )
 
 type ServiceBannerAPI struct {
-	Database database.Store
+	appearanceFetcher *atomic.Pointer[appearance.Fetcher]
 }
 
-func (a *ServiceBannerAPI) GetServiceBanner(ctx context.Context, _ *agentproto.GetServiceBannerRequest) (*agentproto.ServiceBanner, error) {
-	serviceBannerJSON, err := a.Database.GetServiceBanner(ctx)
-	if err != nil && !xerrors.Is(err, sql.ErrNoRows) {
-		return nil, xerrors.Errorf("get service banner: %w", err)
+func (a *ServiceBannerAPI) GetServiceBanner(ctx context.Context, _ *proto.GetServiceBannerRequest) (*proto.ServiceBanner, error) {
+	cfg, err := (*a.appearanceFetcher.Load()).Fetch(ctx)
+	if err != nil {
+		return nil, xerrors.Errorf("fetch appearance: %w", err)
 	}
-
-	var cfg codersdk.ServiceBannerConfig
-	if serviceBannerJSON != "" {
-		err = json.Unmarshal([]byte(serviceBannerJSON), &cfg)
-		if err != nil {
-			return nil, xerrors.Errorf("unmarshal json: %w, raw: %s", err, serviceBannerJSON)
-		}
-	}
-
-	return &agentproto.ServiceBanner{
-		Enabled:         cfg.Enabled,
-		Message:         cfg.Message,
-		BackgroundColor: cfg.BackgroundColor,
-	}, nil
+	return proto.ServiceBannerFromSDK(cfg.ServiceBanner), nil
 }