[chore] increase version and update maintainers

[felixT2K]

This PR:

• increase version to 0.7.0a0 (next release will be minor and not patch)
• add Olivier and myself 😅 also to the list of maintainers

I will cleanup the issue trackers in the next days 👍🏼

Any feedback is welcome 🤗

[codecov]

Codecov Report

Merging #1264 (04ff0a3) into main (f113530) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1264   +/-   ##
=======================================
  Coverage   95.75%   95.75%           
=======================================
  Files         154      154           
  Lines        6901     6901           
=======================================
  Hits         6608     6608           
  Misses        293      293           

Flag	Coverage Δ
unittests	95.75% <ø> (ø)

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[felixdittrich92]

ok issue trackers are updated (for 0.8.0 we can decide later what we want to keep or maybe move to a later release)