TCP support in the Proxy Outpost

**Is your feature request related to a problem? Please describe.**
I run various services like MySQL, PostgreSQL, Redis, ElasticSearch and so on. Sometimes I'd love to expose those services to people who need access to it, but I rather not expose the service itself over the internet.

**Describe the solution you'd like**
I'd love to be able to setup a TCP connection through an Authentik Outpost to my TCP-based services. The idea is that a local port is forwarded through Authentik to the service listening for TCP.

**Describe alternatives you've considered**
Some alternatives do support this, for example:
- Hashicorp Boundary has it, [view this demo](https://developer.hashicorp.com/boundary/docs/getting-started/dev-mode/connect-to-dev-target#connect-using-the-desktop-client).
- Pomerium has [TCP over HTTP](https://www.pomerium.com/docs/capabilities/tcp).

**Additional context**
I'm planning do to authentication through Secret Engines from Vault, for example - using the [MySQL Secret Engine](https://developer.hashicorp.com/vault/docs/secrets/databases/mysql-maria). Might be really awesome to eventually also integrate this into Authentik, but that's not part of this feature request.