Add `worker_main_http_uri` to the contrib bash script (#13772)

* Add worker_main_http_uri, replace >> with >

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>
Co-authored-by: Erik Johnston <erik@matrix.org>

changelog.d/13772.doc

@@ -0,0 +1 @@
+Add `worker_main_http_uri` for the worker generator bash script.

contrib/workers-bash-scripts/create-multiple-generic-workers.md

@@ -7,7 +7,7 @@ You can alternatively create multiple worker configuration files with a simple `
 #!/bin/bash
 for i in {1..5}
 do
-cat << EOF >> generic_worker$i.yaml
+cat << EOF > generic_worker$i.yaml
 worker_app: synapse.app.generic_worker
 worker_name: generic_worker$i
 
@@ -15,6 +15,8 @@ worker_name: generic_worker$i
 worker_replication_host: 127.0.0.1
 worker_replication_http_port: 9093
 
+worker_main_http_uri: http://localhost:8008/
+
 worker_listeners:
   - type: http
     port: 808$i