Add a DitheredObservation type - WIP

[wtgee]

Depends on #735

• Rearrange to support mulitple types of Observations.
• Add a DitheredObservation (coming from AstroHuntsman/huntsman-pocs).

[codecov[bot]]

Codecov Report

Merging #739 into develop will decrease coverage by 0.62%. The diff coverage is 2.77%.

@@             Coverage Diff             @@
##           develop     #739      +/-   ##
===========================================
- Coverage    80.58%   79.96%   -0.63%     
===========================================
  Files           61       62       +1     
  Lines         5188     5182       -6     
  Branches       715      709       -6     
===========================================
- Hits          4181     4144      -37     
- Misses         818      852      +34     
+ Partials       189      186       -3

Impacted Files	Coverage Δ
pocs/scheduler/observation/base.py	94.73% <ø> (ø)
pocs/scheduler/observation/dithered.py	0% <0%> (ø)
pocs/scheduler/observation/__init__.py	100% <100%> (ø)
pocs/base.py

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