Set pkgmeta `<build>` etc. for multiple targets / wildcard support

[jengelh]

Is your feature request related to a problem? Please describe.

I need to disable all Debian targets globally (in the OBS instance). Writing

<build>
<disable repository="Debian_12"/>
<disable repository="Debian_13"/>
<disable repository="Ubuntu_24.04"/>
<disable repository="Ubuntu_25.10"/>
<disable repository="Ubuntu_26.04"/>
</build>

is the canonical way of doing that.

Describe the solution you'd like

<build>
<disable repository="Debian_*"/>
<disable repository="Ubuntu_*"/>
</build>

Describe alternatives you've considered

something with XPath, idk