TSP Client fails on `Content-Type: application/json; charset=utf-8`

### Bug Description:

The current implementation of TSP Client (REST Client) does not accept server replies using `Content-Type: application/json; charset=utf-8` as per [RFC9110 8.3.2 Charset](https://www.rfc-editor.org/rfc/rfc9110#name-charset).

The problem is the strict-equal in https://github.com/eclipse-cdt-cloud/tsp-typescript-client/blob/75cc633cfebf2b15b6b132d4fb50556c28e60fb5/tsp-typescript-client/src/protocol/rest-client.ts#L125

### Steps to Reproduce:

1. Connect to a TSP Server that replies with `Content-Type: application/json; charset=utf-8`
2. See reply to initial `GET /tsp/api/health` to be dismissed due to Content-Type
3. No further requests are being issued

### Additional Information

- Operating System: MacOS 26