MAINT: Add steering committee members to CODEOWNERS

[larsoner]

Hey @mne-tools/mne-python-steering-committee, could each of you please take a moment to open a PR to add yourself to CODEOWNERS in this repo? We would like to start using this as a way to triage issues, PR reviews, and forum posts to people with relevant domain expertise.

Feel free to use as fine-grained or coarse file patterns as you want following the gitignore syntax (see also cheatsheet). To make an example, I've opened a PR on behalf of @rob-luke in https://github.com/mne-tools/mne-python/pull/11972. (And @sappelhoff if you're happy with your current set of files, no need to update anything!)

Progress:

• [x] agramfort
• [x] wmvanvliet
• [x] rob-luke
• [x] drammock
• [x] dengemann
• [x] hoechenberger
• [x] larsoner
• [x] adam2392
• [x] cbrnr
• [x] bloyl
• [ ] mmagnuski
• [x] sappelhoff
• [x] alexrockhill
• [x] jasmainak
• [x] GuillaumeFavelier
• [x] britta-wstnr
• [x] mscheltienne