Add InstrumentTechnique

[agbeltran]

In issue #230 about adding the Technique class and the DatasetTechnique class, there was also a discussion about adding InstrumentTechnique class. In the ICAT collaboration meeting on 10th August 2021, it was decided to create a different issue to track this separate discussion.

It is noted that while the Instrument class contains a type attribute that some facilities use to record the techniques relevant to the instrument, not all facilities use type in this way:
https://repo.icatproject.org/site/icat/server/4.11.1/schema.html#Instrument

For that reason, InstrumentTechnique would not replace the type attribute.

Considerations around overlaps between InstrumentTechnique and DatasetTechnique need to be analysed.