Add .license files for the JSON test artifacts

[ulucinar]

Description of your changes

I had previously worked around the complaining reuse action on some JSON test artifacts by processing the (invalid) JSON documents with license headers in the test itself. Learning a better alternative, this PR proposes to add the .license files.

I have:

• Read and followed Upjet's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Reuse action seems to be happy about the change here and the unit tests are passing here.

[jeanduplessis]

@ulucinar I found a better way to deal with "non-code" file licenses while adding REUSE to crossplane/crossplane: crossplane/crossplane#5251

Look at the .reuse/dep5 file.

It allows you to specify the license for files in a central place rather than adding multiple individual .license files.

[ulucinar]

Observing the deprecation possibility mentioned here, we've agreed to continue with the .license files.

[mergenci]

@ulucinar LGTM.