Splitting KSystemStats out of ksysguard

[Arjen Hiemstra]

Hi,

During the beta phase of Plasma 5.21 there was some discussion with regards to 
what to do with ksysguard now that we are shipping a replacement. Back then, a 
plan was made to ship the ksysguard repo for 5.21 and to split out 
ksystemstats for 5.22.

I spent some time over the last two weeks to do this. We now have a new repo 
located at https://invent.kde.org/plasma/ksystemstats that contains 
ksystemstats and its plugins with appropriate history. Futhermore, the library 
parts to support ksystemstats and its plugins have been moved into 
libksysguard and are now treated the same as other parts of libksysguard, 
which should make it possible to create plugins for ksystemstats outside of 
the ksystemstats repo. Finally, the plugins for the processcore library will 
be moved to libksysguard/processcore/plugins once https://invent.kde.org/
plasma/libksysguard/-/merge_requests/143 has been merged.

With these changes, it should no longer be necessary to ship the ksysguard 
repo for 5.22 and we can move that elsewhere. libksysguard still contains some 
parts that are only of use to the old ksysguard UI, we will be looking at 
moving those into the ksysguard repository at some point in the future.

For the translators: I changed the catalog name for the ksystemstats plugins 
from `ksysguard_global_plugins` to `ksystemstats_plugins`. Apart from the 
mentioned location changes, there should be no other changes to the 
translations.

Cheers,
Arjen