feat: B0 tracker only geometry configuration

[wdconinc]

This PR adds a b0_tracker_only geometry configuration for debugging of B0 tracking issues without loading the whole shebang.

What kind of change does this PR introduce?

• [ ] Bug fix (issue #__)
• [x] New feature (issue #__)
• [ ] Documentation update
• [ ] Other: __

Please check if this PR fulfills the following:

• [ ] Tests for the changes have been added
• [ ] Documentation has been added / updated
• [ ] Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No.

Does this PR change default behavior?

No.