Relax tag requirements when generating changelogs

What does this MR do?

When generating a changelog and leaving out the from parameter, we no longer require that the names of tags start with a "v". Instead, tags can now be in the format X.Y.Z or vX.Y.Z.

This fixes gitlab-com/gl-infra/delivery#1572 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides