Rename `pip_options` / `conda_options` to `options`

While using our `PipInstall` plugin, I noticed that there's a `pip_options` keyword for passing flags to the `pip` CLI.

```python
plugin = PipInstall(["pytorch", "optuna"], pip_options=["--force-reinstall"])
```

Similarly there's a `conda_options` kwarg for `CondaInstall`. Prefixing the name of those kwargs with `pip_` / `conda_` feels a bit redundant with the plugin class name. Renaming `pip_options` / `conda_options` to just `options` would be a bit more ergonomic, while still keeping the intent clear (I think).