.github: workflows: Add C++ linter

[melvo]

PR check list:

• [x] Document your code
• [x] Add \since QXmpp 1.X, QXMPP_EXPORT
• [x] Fix doxygen warnings (see log when building with -DBUILD_DOCUMENTATION=ON)
• [x] Update doc/doap.xml
• [x] Add unit tests
• [x] Format the code: Run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

[melvo]

The action does not support clang-format-15 (only clang-format-14) but the linting tool does.

[codecov[bot]]

Codecov Report

Base: 68.36% // Head: 68.47% // Increases project coverage by +0.11% :tada:

Coverage data is based on head (9fa6206) compared to base (befab2f). Patch has no changes to coverable lines.

:exclamation: Current head 9fa6206 differs from pull request most recent head ba24679. Consider uploading reports for the commit ba24679 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #491      +/-   ##
==========================================
+ Coverage   68.36%   68.47%   +0.11%     
==========================================
  Files         298      292       -6     
  Lines       25869    25653     -216     
==========================================
- Hits        17685    17567     -118     
+ Misses       8184     8086      -98     

Impacted Files	Coverage Δ
src/client/QXmppEntityTimeManager.cpp	12.90% <0.00%> (-2.73%)	:arrow_down:
src/client/QXmppVersionManager.cpp	26.08% <0.00%> (-2.18%)	:arrow_down:
src/base/QXmppDiscoveryIq.cpp	84.61% <0.00%> (-0.18%)	:arrow_down:
tests/qxmppmessage/tst_qxmppmessage.cpp	94.82% <0.00%> (-0.10%)	:arrow_down:
src/base/QXmppMessage.cpp	98.31% <0.00%> (-0.04%)	:arrow_down:
src/omemo/QXmppOmemoManager_p.cpp	5.00% <0.00%> (-0.01%)	:arrow_down:
src/base/QXmppMessage.h	100.00% <0.00%> (ø)
src/client/QXmppClient.cpp	59.80% <0.00%> (ø)
tests/qxmppjingleiq/tst_qxmppjingleiq.cpp	100.00% <0.00%> (ø)
src/client/QXmppMamManager.h
... and 14 more

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[melvo]

clang-format-15 is supported now. Result: Only src/client/QXmppFileSharingManager.cpp seems to need adjustments or maybe .clang-format.

[melvo]

@lnjX This can be reviewed now.