MAINT: reduce hours stefan, clarify lead maintainer

[sappelhoff]

• Reducing my hours due to upcoming commitments that won't allow me to stay involved as much as I was
• Based on internal discussions among maintainers, the role of "lead maintainer" will now be rotating among BIDS maintainers

The role description of what a "lead maintainer" is/does and how we rotate that responsibility should become part of the Maintainers Guide.

Furthermore, the content in the "Maintainers Group" section of the DECISION_MAKING.md document (edited here) should be migrated to the Maintainers Guide, once it's been merged, see:

• 1770

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.04%. Comparing base (898ea86) to head (9142ec9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1843 +/- ## ======================================= Coverage 88.04% 88.04% ======================================= Files 16 16 Lines 1380 1380 ======================================= Hits 1215 1215 Misses 165 165 ```

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