Move requests from optional dev dependencies to regular dependency

[matthewscottgordon]

Related Issue(s):
#477

Description:
Moved the requests dependency from optional-dependencies.dev to dependencies.

The requests package is used by the test_data module which is loaded by load_plugins() when you run stac. I'm not sure if this the right way to fix this; it's possible that that module shouldn't be loaded to begin with.

PR checklist:

• Code is formatted (run scripts/format).
• Code lints properly (run scripts/lint).
• Tests pass (run scripts/test).
• Documentation has been updated to reflect changes, if applicable.
• Changes are added to the CHANGELOG.

[gadomski]

@matthewscottgordon CI failures aren't on you, this repo has a bit of bitrot. I'll try to clean things up today or tomorrow. Thanks for the contribution! After this is merged we can cut a new release.