[release/1.15.3] Add cloud stanza documentation (#17311)

* [CC-4856] Add cloud stanza documentation

* Add environment variables to cloud descriptions

website/content/docs/agent/config/config-files.mdx

@@ -1088,6 +1088,16 @@ Refer to the [formatting specification](https://golang.org/pkg/time/#ParseDurati
 
 - `bootstrap_expect` Equivalent to the [`-bootstrap-expect` command-line flag](/consul/docs/agent/config/cli-flags#_bootstrap_expect).
 
+## Self-managed HCP Parameters
+
+- `cloud` This object specifies settings for connecting self-managed clusters to HCP. This was added in Consul 1.14
+
+  - `client_id` The OAuth2 client ID for authentication with HCP. This can be overridden using the `HCP_CLIENT_ID` environment variable.
+
+  - `client_secret` The OAuth2 client secret for authentication with HCP. This can be overridden using the `HCP_CLIENT_SECRET` environment variable.
+
+  - `resource_id` The HCP resource identifier. This can be overridden using the `HCP_RESOURCE_ID` environment variable.
+
 ## Service Mesh Parameters ((#connect-parameters))
 
 The noun _connect_ is used throughout this documentation to refer to the connect