semver strategy is NOT working as the document claimed

[zywillc]

Describe the bug
current tags filtering behavior will skip semver constraint for prereleases versions (although they are valid semver versions) when there is no explicit constraint parsed from image tags (i.e. empty string) which is inconsistent with the document description.
https://github.com/argoproj-labs/argocd-image-updater/blob/master/pkg/image/version.go#L135-L147

some complex prerelease constraint rules are actually not supported untilsemver > 3.2.0

To Reproduce
Steps to reproduce the behavior:

Expected behavior
follow the truth about semver strategy behavior as the documented and constraint supporting *-0 for prerelease versions

Additional context
fix pr:
#552

Version
0.12.1

Logs
Please paste any relevant logs here