List of requirements for `Scheduler` and `Observation` config

[danjampro]

Scheduler:

• Can ignore targets that have just been observed if necessary
• Can check weather safety, dome status, horizon etc. to determine valid observations
• Can check constraints on individual observations

Observation:

• Can take dithered offset sky pointings in sequence
• Can specify filter name for individual exposures in a compound observation
• Can specify exposure config by camera name to allow for e.g. different filters and exposure times in parallel
• Can have a flag indicating if it has just been observed telling the scheduler to skip it
• Can specify constraints at the observation level

See #466

[wtgee]

Thanks for this. Can we actually write out a sample config that we can then build some code around?