keyboard: add modifier key combination support

[shikl3x7]

Add support for Ctrl+key, Alt+key, Shift+key, Meta+key and multi-modifier combinations in keyboard_write() and keyboard_press().

[chombourger]

The spellcheck action is failing:

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<htmlcontent> docs/usage.rst: html>body>ul>li>ul>li
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Ctrl
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Misspelled words:
<htmlcontent> docs/usage.rst: html>body>ul>li>ul>li
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Ctrl
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Misspelled words:
<htmlcontent> docs/usage.rst: html>body>ul>li>ul>li
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Ctrl
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Misspelled words:
<htmlcontent> docs/usage.rst: html>body>ul>li>ul>li
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Ctrl
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[chombourger]

we also need to fix:

py312: commands[0]> flake8 --exclude 'mtda/scripts,*_pb2.py,*_pb2_grpc.py' mtda mtda-cli mtda-service mtda-www
mtda/main.py:586:13: E731 do not assign a lambda expression, use a def
mtda/main.py:588:17: E131 continuation line unaligned for hanging indent