Change the instrument schema to make the list of collimators a part of detector objects

Change the instrument schema to instead of having a list of **collimators** as a part of the **instrument**, make it part of a **detector** object.

Right now the **collimator** has the **detector** it is attached to as a string inside it, allowing to have **collimators** with the same name if they are attached to different **detectors**. It would be more logical if instead **collimators** would be a part of the **detector** object they are attached to like **links** and **joints** are a part of the **positioner** object.

It would require:
* Update how the Json files are processed into an instrument
* Implement backwards compatibility to be able to read and convert files of old schema into the new one
* Update documentation about the Instrument Schema