chore(sdk): Add StreamrClient#getTheGraphClient() internal method (#3087)

Added a method which provides a client for querying The Graph. All
entities of the Streamr graph can be queried using this client, e.g.:
- `Stream`
- `StreamPermission`
- `Operator` 
- `Sponsorship`
- `Stake`
- `Vote`
- ...

This method is currently internal, but it can be made public if needed.

Needed in #3086.

Author: teogeb

packages/sdk/src/StreamrClient.ts

@@ -759,6 +759,14 @@ export class StreamrClient {
         return this.config
     }
 
+    /**
+     * @deprecated This in an internal method
+     * @hidden
+     */
+    getTheGraphClient(): TheGraphClient {
+        return this.theGraphClient
+    }
+
     /**
      * Get overrides for transaction options. Use as a parameter when submitting
      * transactions via ethers library.