feat(media): add phase5 media provider abstraction and stream credentials APIs

Backend/media/types.ts

@@ -0,0 +1,44 @@
+export type MediaSessionCreateInput = {
+  streamSessionId: string;
+  ownerUserId: string;
+  cameraDeviceId: string;
+  requesterDeviceId: string;
+};
+
+export type MediaPublishCredentials = {
+  provider: string;
+  mediaSessionId: string;
+  publishToken: string;
+  publishUrl: string;
+  expiresInSeconds: number;
+};
+
+export type MediaSubscribeCredentials = {
+  provider: string;
+  mediaSessionId: string;
+  subscribeToken: string;
+  subscribeUrl: string;
+  expiresInSeconds: number;
+};
+
+export type MediaSessionCreateResult = {
+  provider: string;
+  mediaSessionId: string;
+  publishUrl: string;
+  subscribeUrl: string;
+};
+
+export interface MediaProvider {
+  name: string;
+  createSession(input: MediaSessionCreateInput): Promise<MediaSessionCreateResult>;
+  issuePublishCredentials(input: {
+    mediaSessionId: string;
+    cameraDeviceId: string;
+    ownerUserId: string;
+  }): Promise<MediaPublishCredentials>;
+  issueSubscribeCredentials(input: {
+    mediaSessionId: string;
+    viewerDeviceId: string;
+    ownerUserId: string;
+  }): Promise<MediaSubscribeCredentials>;
+}