Create `deployments()`, `observations()` & `media()` to retrieve data

[PietrH]

232

Peter:

Suggested in camtraptor July 2023 coding sprint

Rationale: provide convenience functions to retrieve the tables/data frames from a camtrap dp object, so users don't have to retrieve them from package$data$tablename. Benefits:

Easier to understand than package$data$tablename Retrieving data is an important functionality, so should be tested Can be used by other functions that need to access the data Allows to change data model without affecting functionality Is in line with other suggested functions to retrieve data, such as taxonomy(), locations(), events()

[PietrH]

After discussion we've decided that check_package() should return TRUE for a valid camtrap-dp, or throw errors otherwise. Instead of the current behaviour where it'll return a package object

[PietrH]

Blocked by #247 for check_package(), is used in the new functions where it's expected to return TRUE when there are no issues.

[damianooldoni]

I also allowed GitHub Actions tests to be triggered when we create PRs to the v1.0 branch.