fix: Add missing XML definition of arguments direction for Install and InstallBundle methods

[zaporozhets]

Added missing definition of direction for source argument in Install and InstallBundle dbus methods. It helps sdbus-c++ to generate correct stubs. For example:

Before:

    void Install()
    {
        proxy_.callMethod("Install").onInterface(INTERFACE_NAME);
    }

    void InstallBundle(const std::map<std::string, sdbus::Variant>& args)
    {
        proxy_.callMethod("InstallBundle").onInterface(INTERFACE_NAME).withArguments(args);
    }

After:

    void Install(const std::string& source)
    {
        proxy_.callMethod("Install").onInterface(INTERFACE_NAME).withArguments(source);
    }

    void InstallBundle(const std::string& source, const std::map<std::string, sdbus::Variant>& args)
    {
        proxy_.callMethod("InstallBundle").onInterface(INTERFACE_NAME).withArguments(source, args);
    }

[codecov]

Codecov Report

Merging #786 (6e5c832) into master (1564c3a) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #786      +/-   ##
==========================================
- Coverage   72.85%   72.84%   -0.02%     
==========================================
  Files          28       28              
  Lines        8798     8798              
==========================================
- Hits         6410     6409       -1     
- Misses       2388     2389       +1     

Impacted Files	Coverage Δ
src/main.c	75.41% <0.00%> (-0.09%)	⬇️

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[ejoerns]

I've slightly adapted the commit message's title to better match our conventions.

Otherwise, looks fine for me. Good catch and thanks for your Contribution! 👍

Note: Accept despite CI fails (unrelated known issue).