Added validation tag field to provide validation regex together with a tag.
Update kaniko-build-config.yaml to provide default tag for pr and commit images with validation regex.
Validating tag when parsing it's value.
Added TagOption to add PR number to the Tagger instance.
Using pull request default tag together with user provided tags instead replacing all values with default tag. This allows users to provide their own tag to the images build on pr.

Set only tagger fields needed for image type.
Fix validation regex for commit to align with expected date format.
Return error from TagOption to signal problems with setting it.
Checking if pr or sha strings passed to TagOption is empty. Return error when trying to set empty string.

Added validation tag field to provide validation regex together with a tag.
Update kaniko-build-config.yaml to provide default tag for pr and commit images with validation regex.
Validating tag when parsing it's value.
Added TagOption to add PR number to the Tagger instance.
Using pull request default tag together with user provided tags instead replacing all values with default tag. This allows users to provide their own tag to the images build on pr.

Set only tagger fields needed for image type.
Fix validation regex for commit to align with expected date format.
Return error from TagOption to signal problems with setting it.
Checking if pr or sha strings passed to TagOption is empty. Return error when trying to set empty string.

Small fixes in application.

…nto custom-tag-on-pr

# Conflicts:
#	cmd/image-builder/main.go
#	pkg/tags/tag.go

Added tests for options.

…-tag-on-pr