search: use an alert and suggestion when OOM-like behavior surfaces

Created by: rvantonder

It's not currently possible to surface an alert in searcher since it can't be propagated back. That would be the preferred solution.

Instead, I'm relying on the error string here to promote it to an alert instead, as before. It's either this, or I can completely suppress the error and only log it, and return "no results".

Created by: codecov[bot]

Codecov Report

Merging #7187 into master will increase coverage by 0.02%. The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #7187      +/-   ##
=========================================
+ Coverage   39.18%   39.2%   +0.02%     
=========================================
  Files        1228    1230       +2     
  Lines       64162   64164       +2     
  Branches     6036    6066      +30     
=========================================
+ Hits        25140   25155      +15     
+ Misses      36722   36709      -13     
  Partials     2300    2300

Impacted Files	Coverage Δ
cmd/searcher/search/search_structural.go	93.54% <100%> (+0.1%)
cmd/frontend/graphqlbackend/search_results.go	54.37% <100%> (+0.26%)
cmd/frontend/internal/cli/http.go	0% <0%> (ø)
lsif/src/server/routes/lsif.ts	7.33% <0%> (ø)
lsif/src/shared/models/xrepo.ts	100% <0%> (ø)
web/src/enterprise/repo/settings/backend.tsx	0% <0%> (ø)
lsif/src/server/settings.ts	100% <0%> (ø)
...iptions/SiteAdminCreateProductSubscriptionPage.tsx	0% <0%> (ø)
web/src/enterprise/site-admin/routes.ts	0% <0%> (ø)
lsif/src/worker/worker.ts	0% <0%> (ø)
... and 32 more