Add -i/--include option to "generate" CLI command.

[libklein]

Currently, it is not possible to include additional character in the "generate" CLI command. This PR fixes this.
It adds -i/--include to the generate cli and sets the additional character set accordingly.
Here, it mimics the behavior of the GUI: The default character set is used if the generator is not constrained otherwise.

Testing strategy

Add two tests to TestCli. First test tests that additional characters are included, second asserts that the default character set is used unless specified otherwise.

Open questions

• Currently the "generate" command does not check the specified length against the minimum length required (i.e., with the "from every group" option). Is this a bug?
• Should there be an something like an --include-exclusive option? Which uses only the characters given in the argument?
• The GUI and password generator do not include the "additional characters" group in the minimum length computation (https://github.com/keepassxreboot/keepassxc/blob/develop/src/core/PasswordGenerator.cpp#L303 and https://github.com/keepassxreboot/keepassxc/blob/develop/src/gui/PasswordGeneratorWidget.cpp#L580). Is this a bug?
• Should we remove the minimum length computation from the GUI and just rely on PasswordGenerator.isValid()? That would be a dependency less.

Type of change

• ✅ New feature (change that adds functionality)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 4 lines in your changes missing coverage. Please review.

Project coverage is 64.24%. Comparing base (d3b28f8) to head (d834432).
Report is 558 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/gui/PasswordGeneratorWidget.cpp	50.00%	3 Missing ⚠️
src/core/PasswordGenerator.cpp	96.67%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7112      +/-   ##
===========================================
+ Coverage    64.21%   64.24%   +0.03%     
===========================================
  Files          334      334              
  Lines        42221    42194      -27     
===========================================
- Hits         27111    27107       -4     
+ Misses       15110    15087      -23     

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