Clarify options for placement of solar collectors on PlantLoops: demand side? Supply side? Both

[jmarrec]

Issue overview

This came up again in #7721 (comment):

Lots of confusion on what the placement of solar collectors should / must be.
Generally speaking the documentation and example files in E+ seem to imply demand side placement (with control of the loop via availability managers).

OpenStudio forces you to put the Flat Plate ones on the supply side (for some reason...) and it appears to work fine too.

References:

• https://unmethours.com/question/27837/which-side-of-the-plant-loop-for-solar-collector-in-eopenstudio/
• solar collectors are not allowed on the demand side of plant loops OpenStudio#2880
• IntegratedCollectorStorage object being incorrectly added to the PlantEquipmentList OpenStudio#3761 (comment)

Details

Some additional details for this issue (if relevant):

• Platform (Operating system, version): Any
• Version of EnergyPlus (if using an intermediate build, include SHA): 9.2.0

Checklist

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• Defect file added (list location of defect file here)
• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)