[backend] adding appstream.xml and appstream-icons to match appstream-generator requirements

[doccaz]

Fixing publisher code to also generate the appstream.xml and appstream-icons.gz files, to match what appstream-generator and everything that uses appdata look for (like Gnome Software) in recent releases.
We're also changing the way Leap 15.2 and Tumbleweed look for appdata to match this, as proposed in DimStar77/openSUSE-appstream#2

As discussed in #8999 .

[adrianschroeter]

You are aware that the publisher is not creating the factory repository of the products?
So for the particular repo it is the wrong code.

It is also potential incompatible, but maybe okay. Are we sure that old code streams and tooling is not stumbling over the new file? We may need a configuration option otherwise ...

Please prefix your commit with [backend] tag.

thanks!

[adrianschroeter]

Does it make to have both files at the same time at all?

Otherwise I would go with a config option instead...

[doccaz]

You are aware that the publisher is not creating the factory repository of the products?
So for the particular repo it is the wrong code.
I didn't know that. Who creates the appdata for factory?

Please prefix your commit with [backend] tag.
Done.

[doccaz]

Does it make to have both files at the same time at all?

Yes, it already does a copy of appdata to appease both SLE12 and SLE15. What transpired from issue #8999 is that the filenames are different for the latest appstream specification.

Otherwise I would go with a config option instead...
Someone else suggested adding a prjconf option to generate appdata (and the required format). I don't know my way around the UI code, though.

[codecov]

Codecov Report

Merging #9019 (5f563b0) into master (9599aa5) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9019      +/-   ##
==========================================
- Coverage   90.98%   90.98%   -0.01%     
==========================================
  Files         513      513              
  Lines       21118    21118              
==========================================
- Hits        19215    19214       -1     
- Misses       1903     1904       +1     

[mlschroe]

What "latest appstream specification"? Such a thing does not really exist for the repository metadata.