[#266] Orbital element observations

[Mark2000]

Description

Closes #266

Adds orbital element observations.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How should this pull request be reviewed?

• By commit
• All changes at once

How Has This Been Tested?

Added some tests.

Checklist

• I have performed a self-review of my code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation and release notes
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[LorenzzoQM]

Nice addition! It should be good to merge after adding the unit for the inclination (to avoid any possible confusion).