Related Issue(s):

• Uses code from Item builder stac-utils/stactools#268
• Prerequisite for Support generating metadata from astraea-opendata COGs #70

Description:
In an effort to refactor this package to easily extend it to support #70, this PR refactors the item creation code to use a new Builder pattern. The builder pattern is defined in a stactools.builder namespace, which yanks code from stac-utils/stactools#268. I think this is a good real-world exercise of the builder pattern, with the hopes that lessons learned here can be moved back to stactools.

This is a non-breaking change, there's no real changes to the generated STAC objects (just a couple of trivial re-orderings of the attributes).

I did deprecate two of the COG-creation functions, since they have been superceded by the builder. The deprecation remarks that the functions will be removed in v0.4.0 (two "major" releases from now).

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.
• Example STAC Catalog has been updated to reflect changes, if applicable.
• Changes are added to the CHANGELOG.