fix: improve search UX on initial store load

[abbiesims]

Done

Fixes #4822
Allows user to search for a snap outside of the featured snaps on initial load of the store.

How to QA

Go to https://snapcraft-io-4843.demos.haus/store and check:

1. Initial load shows featured snaps as normal
2. Selecting a category filters snaps correctly
3. Deselecting a category returns UI to show Featured snaps
4. Entering a search term allows user to search through all snaps
5. Selecting a category with a search term filters the search to the chosen category (and vice versa)

Testing

• This PR has tests
• No testing required (explain why): no new features - updated existing tests

Issue / Card

Fixes https://warthogs.atlassian.net/browse/WD-14710

[webteam-app]

Demo

Jenkins

demos.haus

[steverydz]

When searching all snaps the heading is still "Featured snaps". Perhaps this should change to "All snaps" or just "Snaps"?

[abbiesims]

When searching all snaps the heading is still "Featured snaps". Perhaps this should change to "All snaps" or just "Snaps"?

Nice catch 👍 will change it to just "Snaps" so that when a filter is also selected it doesn't say "All...", think that makes the most sense.

[steverydz]

LGTM 👍