Update Docs for retirement of SLSA v0.2 and new default of v1.0

What does this MR do?

Removes what appears to be an outdated statement that only zip files are covered by the SLSA support (I've done it for an arbitrary binary file)

The sample SLSA attestion is v0.2 which was supposed to have been removed in GitLab 17 and the new default is v1.0

I am attaching a recent SLSA 2.0 attestation generated by a pipeline. It has a very different structure to the v0.2 example - so not sure how that should be reconciled?

It shows two files, which is helpful to show that it works for multiples.

artifacts-metadata.json

Related issues

#367203 (closed) - closed, but referenced in the docs as active.

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