vulnerability

currently we have a version selector for every git tag, which is unnecessary overhead on the user. It is not needed from documentation perspective as there aren't (shouldn't be) any docs change in patch versions, only for new/changed features.

before:
v0.27.0, v0.27.1, v0.27.2, v0.28.0
after
v0.27, v0.28

What would you like to be added:
A new command grype update
Why is this needed:
It would make the update process a lot easier. Grype already knows if you are running an outdated version.
Additional context:
Example output

$ grype <image_name>
New version of grype is available: 0.44.0 (currently running: 0.41.0)
You can update grype to the latest version running '