Create product specs set upon navigation if `id` is unset.

*video demo in bug comments

1. If there's an `id` in URL's search parameters, fetches set
   associated with it & uses that to populate table.
2. If there's no `id` in URL's search parameters (but there are urls),
   create a set, so that #1's behavior can be used for subsequent page
   loads AND add id to url's search parameters.

Change-Id: Iec5c97bf7b77fbc7b0f95adaeaa036832bc55d8f
Bug: 338118596,337334372
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5506871
Commit-Queue: Paul Adedeji <pauladedeji@google.com>
Reviewed-by: Brendon Tiszka <tiszka@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1297559}