Relax PySTAC dependency

[gadomski]

Related Issue(s):

• Closes update pystac dependency for 1.3 release #138
• Closes Error when listing collections - tries to use local directory as self href #113

Description: Relaxes the PySTAC dependency to allow 1.3 (and above). Includes:

• Upgrades to setup-python@v3 and its built-in cache support
• Checks CI against any pre-release versions of PySTAC
• Checks CI against the minimum versions of all dependencies

See this post for some background on the CI setup.

Note: We may want to add min-versions and pre-release to the required checks for pull requests?

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG