Redirect aggregated cluster URLs to main search page so that bots stop causing errors by crawling those fake URLs

[mnaydan]

This should help us with #597

testing notes

• [x] archive search urls with multiple clusters should redirect to the main archive search with no additional parameters (sample test url)
• [x] archive search should work normally without a cluster parameter (does not redirect)
• [x] search within a single cluster should work as before (does not redirect)

[mnaydan]

I tested with your sample URL & this one and they both redirect to main search as expected. I also tested by clicking on a cluster, then clicking "Search the full archive" which is how we produced the problem URL, and it redirects to main instead as expected (I think this was included in the last production release). (Note that the problem URL is still a valid URL: https://test-prosody.cdh.princeton.edu/archive/?cluster=&page=1 -- will that be an issue?

As far as I can tell, main search and search within cluster work normally (do not redirect).

[mnaydan]

Rebecca confirmed that the empty cluster param is equivalent to no cluster param and should not cause an issue, so we can close!