(core) support a wildcard option for ALLOWED_WEBHOOK_DOMAINS

Summary:
Now that webhook payload delivery can be done using a proxy,
it may be desirable to no longer require a set of `ALLOWED_WEBHOOK_DOMAINS`.
This diff allows this variable to be set to `*`. With this setting,
any domain, and both `http` and `https` protocols will now be accepted.

Another possibility would be to default to unchecked
behavior if `ALLOWED_WEBHOOK_DOMAINS` is not set. But this would
introduce a new kind of vulnerability to unconfigured Grist
installations.

Test Plan: switched a test from naming a domain to using `*`

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3903

app/server/mergedServerMain.ts

@@ -141,6 +141,7 @@ export async function main(port: number, serverTypes: ServerType[],
 
   server.finalize();
 
+  server.checkOptionCombinations();
   server.summary();
   return server;
 }