fix(data-store-json): order credentials with weird issuanceDate

[mirceanis]

What is being changed

Some credentials from the wild are missing an issuanceDate, or have the date in a non-parseable format.
This fix defaults their date to unixtime(0) when compared to other credentials for database sorting.

Quality

Check all that apply:

• I want these changes to be integrated
• I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
• I allow my PR to be updated by the reviewers (to speed up the review process).
• I added unit tests.
• I added integration tests.
• I did not add automated tests because only the data-store-json plugin accepts undefined issuanceDate.

Details

I added #1274 to demonstrate how a test for this might look like, but it would introduce a breaking change (if people use their own migrations)