Incorrect parsing of image URL provided in the command line

**What steps did you take:**
Try to pull a bundle while providing the protocol (e.g. `https://`, `http://`) as part URL fails with a strange error

**What happened:**
```
imgpkg pull -b https://index.docker.io/k8slt/demo-repo@sha256:aef6d96cde8e41fbdd67202106c89a5c55bd0cd47398de619a60a4ae06a3e388 -o /tmp/lol
Error: Checking if image is bundle: Collecting images: Working with https://index.docker.io/k8slt/demo-repo@sha256:aef6d96cde8e41fbdd67202106c89a5c55bd0cd47398de619a60a4ae06a3e388: Get "https://https/v2/": dial tcp: lookup https on 10.21.82.100:53: no such host
```

**What did you expect:**
The bundle to be pulled. If you execute without the protocol is works
```
imgpkg pull -b https://index.docker.io/k8slt/demo-repo@sha256:aef6d96cde8e41fbdd67202106c89a5c55bd0cd47398de619a60a4ae06a3e388 -o /tmp/lol
Pulling bundle 'index.docker.io/k8slt/demo-repo@sha256:aef6d96cde8e41fbdd67202106c89a5c55bd0cd47398de619a60a4ae06a3e388'
Extracting layer 'sha256:34de6e22982f89d95517c1cdb76e4d81f6a0735c78f89c56ab7a627b785b0aad' (1/1)

Locating image lock file images...
One or more images not found in bundle repo; skipping lock file update

Succeeded
```

**Anything else you would like to add:**
[Additional information that will assist in solving the issue.]

**Environment:**

- imgpkg version (use `imgpkg --version`): 0.8.0
- Docker registry used (e.g. `Docker HUB`): docker hub, but is unrelated
- OS (e.g. from `/etc/os-release`): MacOS

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We are also happy to receive and review Pull Requests if you want to help to work on this issue.

Start by reproducing the reported `imgpkg pull -b https://...` command and compare it with the working command without the protocol. Trace the `imgpkg pull` URL parsing and registry request path, then add regression coverage showing that `http://` and `https://` bundle URLs are accepted and pulled successfully without breaking protocol-less URLs.

Written by the indexing model from the issue text.