Migrate server to ESM

Sorry for the very big commit that may lead to git log issues and merge
conflicts, but it's a major step forward:

 * Server can be faster at startup because imports() are async and we can
   easily lazy import big modules
 * Angular doesn't seem to support ES import (with .js extension), so we
   had to correctly organize peertube into a monorepo:
    * Use yarn workspace feature
    * Use typescript reference projects for dependencies
    * Shared projects have been moved into "packages", each one is now a
      node module (with a dedicated package.json/tsconfig.json)
    * server/tools have been moved into apps/ and is now a dedicated app
      bundled and published on NPM so users don't have to build peertube
      cli tools manually
    * server/tests have been moved into packages/ so we don't compile
      them every time we want to run the server
 * Use isolatedModule option:
   * Had to move from const enum to const
     (https://www.typescriptlang.org/docs/handbook/enums.html#objects-vs-enums)
   * Had to explictely specify "type" imports when used in decorators
 * Prefer tsx (that uses esbuild under the hood) instead of ts-node to
   load typescript files (tests with mocha or scripts):
     * To reduce test complexity as esbuild doesn't support decorator
       metadata, we only test server files that do not import server
       models
     * We still build tests files into js files for a faster CI
 * Remove unmaintained peertube CLI import script
 * Removed some barrels to speed up execution (less imports)

scripts/simulate-many-viewers.ts

@@ -1,5 +1,5 @@
 import Bluebird from 'bluebird'
-import { wait } from '@shared/core-utils'
+import { wait } from '@peertube/peertube-core-utils'
 import {
   createSingleServer,
   doubleFollow,
@@ -7,7 +7,7 @@ import {
   PeerTubeServer,
   setAccessTokensToServers,
   waitJobs
-} from '@shared/server-commands'
+} from '@peertube/peertube-server-commands'
 
 let servers: PeerTubeServer[]
 const viewers: { xForwardedFor: string }[] = []