Cryptic error message when copying tar to repository

**Describe the problem/challenge you have**
When copying a tar, or a bundle to a repository, when the destination provided in the command line contains a tag, or have no repository, or is malformed in some way the error message is not very helpful
ex:
```
imgpkg copy --tar some-bundle-v0.1.0.tar --to-repo localhost:5000
Error: Building import repository ref: repository can only contain the runes `abcdefghijklmnopqrstuvwxyz0123456789_-./`: localhost:5000
```

**Describe the solution you'd like**
`imgpkg` should be able to replace the message that is provided by the ggcr library with an easier understand message.
When a tag is present it should say: `cannot specify a tag in the destination repository`
When is malformed it should say `destination repository is not valid. The format allowed is registry.io/some-image or registry.io:11111/some-image`

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