feat: make ``load_credentials_from_file`` a public method (#530)

* feat: make load_credentials_from_file public and alllow scopes

* test: update tests

* fix: raise error for json with no type

* test: fix test names

* refactor: simplify control flow

* fix: raise coverage

* test: update test

Co-authored-by: arithmetic1728 <[email protected]>
Co-authored-by: Sijun Liu <[email protected]>
3 files changed