add default CORS middleware

[geospatial-jeff]

Related Issue(s):

• Closes Provide default CORS middleware #436

Description:
Adds a subclass of starlette's standard CORS middleware w/ defaults set to those recommended by the stac spec. Added the CORS middleware to default set of middleware used by the application.

PR Checklist:

• Code is formatted and linted (run pre-commit run --all-files)
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.

[captaincoordinates]

I understand why you closed #341 but I think you should consider bringing in those unit tests, as this is currently untested.

[geospatial-jeff]

Will do!