Add docker tags for major/minor/patch versions

[Quadrubo]

Description

As of the point of writing this, v2.11.0 is the latest ntfy version.
As I'm manually updating my images and not using something like "latest", I have to change the image tag every new release. It would be nice if I wouldn't have to do that for patch releases (minor releases too).

Currently these tags are provided:

• v2.11.0 - Version 2.11.0
• v2.10.0 - Version 2.10.0
• latest - Version 2.11.0

Desired Behavior

I would propose a tag system like this:

• v2.11.0 - Version 2.11.0
• v2.10.0 - Version 2.10.0
• v2.11 - Version 2.11.0
• v2 - Version 2.11.0
• latest - Version 2.11.0

This would allow pinning to specific version and allows the user to choose which semver types they are okay with auto updating.
I for example would have pinned to v2 and would have automatically gotten the update to v2.11.0.
I however will not get the automatic update to v3.x which would be desired for me.