Fix TNS API credentials security.

[genghisken]

This issue is identical to the one in the lasair-lsst code base. Replicated here, because the similar code needs a similar fix.

The sequence of events is:

• Merge existing lasair-lsst and lasair-lsst-dev code hotfix into main. Deploy onto the lasair-lsst and lasair-lsst-dev areas. The latter involves also merging the hotfix into the develop branch.
• Fix THIS lasair4 code base (main) to similarly hide the token.
• Update the API key on TNS.
• Update the API key in Vault.
• Deploy the new key into settings.py on the svc nodes in lasair-ztf, lasair-lsst-dev and lasair-lsst.
• Restart the TNS poller.