WIP: Add lastModified field to generated index file

[Jdubrick]

Please specify the area for this PR

What does does this PR do / why we need it:
This is the first PR aimed at supporting a lastModified query parameter for filtering data. The changes made as part of this PR add functionality for reading a last_modified.json file that is added to the registry directory during build. The goal is to read these values and assign them to their proper stack/sample versions they belong to within the generated index file.

In addition to this functionality I had to do more data manipulation to allow for the proper setting of these values, it is easier to do this in go rather than bash so it was done here instead of devfile/registry#429.

Additionally, tests were updated to contain the new field so we can ensure it is being added correctly.

FYI changes still need to be made on the index/server side for the actual endpoint, this is just the index/generator work for the index file.

Which issue(s) this PR fixes:

fixes devfile/api#1327

PR acceptance criteria:

• Test Coverage
  • Are your changes sufficiently tested, and are any applicable test cases added or updated to cover your changes?

Documentation (WIP)

• Does the REST API doc need to be updated with your changes?
• Does the registry library doc need to be updated with your changes?

How to test changes / Special notes to the reviewer:
Go tests should pass - The new field was added to the expected index file.

[openshift-ci]

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[Jdubrick]

I added the gosec exemption as it is following and cleaning the path the same as the following:
https://github.com/devfile/registry-support/blob/main/index/generator/library/library.go#L412
https://github.com/devfile/registry-support/blob/main/index/generator/library/library.go#L545
https://github.com/devfile/registry-support/blob/main/index/generator/library/library.go#L633

[Jdubrick]

https://github.com/devfile/registry-support/actions/runs/9617745553/job/26530169277?pr=248 should be resolved after devfile/registry#429 is merged

[Jdubrick]

Going to close - I'll open a new PR with the index/server changes. It will be too much of a headache to have them in separate PRs for tests