fix: install IActsGeoSvc.h into <prefix>/include/k4ActsTracking/IActsGeoSvc.h

[wdconinc]

This installs the interface header in the right place for use by downstream projects.

BEGINRELEASENOTES

• Install interface header into suitably prefixed directory

ENDRELEASENOTES

[wdconinc]

@Zehvogel FYI (not sure you have this repo setup to notify you of new PRs)

[Zehvogel]

Hi @wdconinc, thanks for the contribution! Can you rebase this if you get the chance?
This was somewhat further down my list as this repo is not in the key4hep-stack at the moment... so does this PR mean you plan to use it? :)

@andresailer can you take a look? It looks alright to me but my cmake knowledge is limited.

[wdconinc]

Yes, we've moved over to using k4FWCore for our Gaudi-based components, and we would like to move out Acts geo service into k4ActsTracking. Since we're already using this for Acts tracking in production, I'm hoping it will be useful for you if we upstream it.

[wdconinc]

Rebased.

[wdconinc]

I'll check what's going on with the failing tests, but might be a few days due to travel.

[paulgessinger]

The generated cmake config file does not seem to be found by the downstream cmake build.