Add SQLite support for building ITkPixel Readout Geometry

As title, allows SQLite-based building of ReadoutGeometry for ITk Pixel.

A few things become apparent when working on this that should be improved later (mentioned here for documentation):

• The block doing loop over the FullPhysVols and create the SiDetectorElements is identical to (part of) the same method in the equivalent ITkStrip code, with the exception of the prefix that should be searched for (here RD53_, for strips RG_). It therefore might be better to pull this out into a common util that can be configured and used by both.
• Both this and the ITkStrip look for a node called "GeoModelXML" which is determined by the name of the plugin used to produce the input file (currently common for both). In future we may want to have separate plugins that name things differently, so it would be good to be able to set the node via a python configurable
• However, since the GmxInterface is not based on any Athena base class, we cannot directly set properties for this, and so we would need to find an elegant way to pass the necessary values through from some configured component (such as the DetectorTools) in order to be able to address both the above points

FYI @sroe @hhayward @jmasik @dshope @boudreau @tsulaia