model: validate unique bundle versions

[joelanford]

Description of the change:
Validate that bundles within a package use unique semver versions.

Motivation for the change:
This has always been assumed. Now we are explicitly checking.

I verified that the operatorhubio catalog and all of Red Hat's catalogs for OCP 4.15 and 4.16 continue to pass with this new validation.

Are there any other catalogs that should be checked?

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: joelanford

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[codecov]

Codecov Report

Attention: Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 48.22%. Comparing base (e787595) to head (0f175eb).
Report is 3 commits behind head on master.

Files	Patch %	Lines
pkg/api/api_to_model.go	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1417      +/-   ##
==========================================
+ Coverage   48.14%   48.22%   +0.07%     
==========================================
  Files         136      136              
  Lines       12780    12805      +25     
==========================================
+ Hits         6153     6175      +22     
- Misses       5593     5595       +2     
- Partials     1034     1035       +1     

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[grokspawn]

/lgtm