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`.