Add support for History operation

[jhlee-mitre]

Major changes:

1. Added TestScripts and fixtures for Observation Resource
2. Added TestScript and testing codes for history
3. Updated read.me

[ms-k1ngk0ng]

• I would rename this PR to be more descriptive about what it's accomplishing. Something like 'Add support for History operation'.
• We should hide the TestReports directory from git. I think it's excessive to push up every TestReport we create -- especially if running the engine will just recreate them anyways.
• The opposite for TestScripts -- let's keep pushing up every new, unique TestScript we find/create.
• We need to solidify on our naming conventions for both TestScripts and TestReports. I know that probably seems excessive and semantic at this point, but I think it's gonna help keep us organized in the long run. I'll start a Slack thread about it.
• Last, we need to get back in the habit of writing unit tests. The ones we have are .... less than stellar. I'm going to get you started on some unit tests specifically for history and then push them up and let you take them over the finish line @jhlee-mitre. And then in the near future, you'll have the joy of rewriting our existing tests, which will help us cover our bases and confirm that what we have works well.

Thrilled to have you working on this and keep pushing it forward 👍

[jhlee-mitre]

Accepted Jack's suggestions. Read.me content has rooms for improvement.