Notify users of updated versions

[mike-gangl]

Users may not be using the awesome new functionality of the subscriber! let them know that a new version exists when applicable. Will require a user to grab the version with this capability before they get notified...

Assumptions
release tags will always use semantic versioning: 1.7.0, 1.7.1, 1.9.0, etc

Github releases API
curl -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/podaac/data-subscriber/releases

Semantic versioning comparison
as seen here: https://stackoverflow.com/questions/11887762/how-do-i-compare-version-numbers-in-python

>>> from packaging import version
>>> version.parse("2.3.1") < version.parse("10.1.2")

[mike-gangl]

Merged into develop. Will be available with 1.13.0 release.