Config option for toolset prefiltering (#1293)

A recent change (#1196) introduced the framework for prefiltering
toolsets based on the compatibility of the configured target(s). The
initial implementation included a filter to expose the `projects_list`
tool based on whether any target is OpenShift or not. This functionality
was always on, which was problematic in certain setups.

This change gates this functionality behind a config option:

```
experimental_enable_target_compatibility_tool_filters = true
```

As implied by the name, we consider the feature experimental, and will
rename/redesign/remove the config option in the future.


Co-Authored-By: claude

Signed-off-by: Eric Fried <efried@redhat.com>