various updatecli compose fixes

[olblak]

While working on https://github.com/olblak/updatecli-policy-docusaurus
I spotted a few issues which I am collecting and fixing in this pullrequest

• fix: compose file should work without oci policies
• fix: latest tag shouldn't return the oldest tag
• fix: used sanitize policy version for before push to ensure that v prefix are removed
• fix: various path scenarios when publishing policies

Test

To test this pull request, you can run the following commands:

cd <to_package_directory>
go test

Additional Information

Tradeoff

Potential improvement