Separate interfaces and API client to be separate installables

Since the initial project was started I've expanded the scope to include a #13 and now #25 `terminal` based interface to interact with the Gallagher ecosystem.

While this is super cool we should pollute the install base with unnecessary items if the all the user wants is the API client.

We propose to split the installables into three (or as many as required into the future):
- `gallagher`, installs the API client only
- `gallagher[cli]`, installs the CLI which will require the API Client
- `gallagher[gui]`, installs the textual based interfaces
- `gallagher[all]` installs everything we offer

> Note this requires a refactor of the `pyproject.toml` file

Example from @taskiq-python projects can be [found here](https://github.com/taskiq-python/taskiq-faststream/blob/develop/pyproject.toml)