feat(helm/provisioner): support deploying multiple provisioners in same namespace (#15637)

Fixes https://github.com/coder/coder/issues/15437

- Adds support for `coder.serviceAccount.disableCreate` (originally
added to `helm/coder` in https://github.com/coder/coder/pull/14817).
- Adds documentation and examples in `helm/provisioner/README.md` on
deploying multiple provisioners in the same namespace leveraging
`nameOverride`.

helm/coder/values.yaml

@@ -113,7 +113,7 @@ coder:
     annotations: {}
     # coder.serviceAccount.name -- The service account name
     name: coder
-    # coder.serviceAccount.name -- Whether to create the service account or use existing service account
+    # coder.serviceAccount.disableCreate -- Whether to create the service account or use existing service account.
     disableCreate: false
 
   # coder.securityContext -- Fields related to the container's security