Clarify the Snapshots used in Tests

## Is Your Feature Request Related To A Problem? Please describe.

For the Pester Tests, we have a few `ChocolateySnapshot` helper functions. It's not immediately clear what they're for, or which case warrants which function.

## Describe The Solution. Why is it needed?

It seems that most times we don't need the `New-ChocolateySnapshot` function and instead should be using `Restore-ChocolateySnapshot`. If there are no cases where we would actually need to move up the stack of snapshots, then the proposal would be to remove the `Restore-ChocolateySnapshot` function and update `New-ChocolateySnapshot` to do the removal of previous snapshots first...

At the very least we should better document what the snapshotting is doing, and how to make use of it in tests.

## Additional Context.

Working on adding tests for the licensed extension and we ran into some confusion as to which one to use when.

## Related Issues

https://gitlab.com/chocolatey/build-automation/chocolatey-test-kitchen/-/issues/16

Start by locating the Pester test helpers named New-ChocolateySnapshot and Restore-ChocolateySnapshot and read their current behavior. Document what each snapshot function is for and which test situations require it; if the proposed simplification is valid, record the expected helper changes and update affected tests.

Written by the indexing model from the issue text.