search: add stable parameter

Created by: rvantonder

Stacked on #9680. Adds stable parameter to ensure deterministic result ordering. Uses pagination underneath the hood.

Notes

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@slimsag This will use a default result count of 30, since that's in line with current search. But, if the intuition about the behavior here is that it should be lower, LMK.

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Ran into the 5K limit for pagination requests, and I think that makes sense to keep. To wit, you'll get this alert,

instead of

when using stable:. There's probably a better way to phrase the alert, but the point is it's better than AH-A-RED-ALERT-WHAT-DOES-IT-MEAN.

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This PR also makes limitHit significant to clients who might care about it (like our webapp, which depends on it to surface the 'show more' link/buttons). For pagination, we simply give the meaning to limitHit as "pagination has not reached the final cursor for this request'.

Then we get this, as desired: