(core) Enabling telemetry on /api/version endpoint

Summary:
Version API endpoint wasn't logging telemetry from POST requests. The issue was in registration
order, this endpoint was registered before `expressJson` and it couldn't read json body in the handler.

Test Plan: Added new test

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D4277

app/server/lib/FlexServer.ts

@@ -1971,7 +1971,7 @@ export class FlexServer implements GristServer {
   }
 
   public addUpdatesCheck() {
-    if (this._check('update')) { return; }
+    if (this._check('update', 'json')) { return; }
 
     // For now we only are active for sass deployments.
     if (this._deploymentType !== 'saas') { return; }

app/server/lib/UpdateManager.ts

@@ -85,15 +85,12 @@ export class UpdateManager {
       const payload = (name: string) => req.body?.[name] ?? req.query[name];
 
       // This is the most interesting part for us, to track installation ids and match them
-      // with the version of the client. Won't be send without telemetry opt in.
+      // with the version of the client.
       const deploymentId = optStringParam(
         payload("installationId"),
         "installationId"
       );
 
-      // Current version of grist-core part of the client. Currently not used and not
-      // passed from the client.
-
       // Deployment type of the client (we expect this to be 'core' for most of the cases).
       const deploymentType = optStringParam(
         payload("deploymentType"),