Frontend: Add web smoke tests

[umpox]

Description

We want to add frontend smoke tests that can quickly check basic Sourcegraph functionality to ensure our application is working correctly after a deployment.

Acceptance criteria

• [x] The smoke tests assert:
  • [x] The frontend code delivers its bundle and does not serve a blank page.
  • [x] A very basic (very quick) search is returning some results
  • [x] The results should be stable and loose enough so the assertion stays true across time even if new code is indexed by Sourcegraph.
• [x] The smoke tests are fast (<2m ?)
• [ ] The smoke tests are not flaky.
  • (across 100 runs, we should always get the same test result)
• [x] The smoke tests are not dependent on the sourcegraph/sourcegraph repo. The tests should be published to NPM, so we can run them without having to clone these repo.
• [x] We can run the tests through a single command (e.g. npx @sourcegraph/smoke-test --url=https://sourcegraph.com)

Prior context

See https://github.com/sourcegraph/sourcegraph/issues/31859 for further context on this issue.

A experimental PR that may be relevant is here: https://github.com/sourcegraph/sourcegraph/pull/29620. Note: This PR predates the issue above, so will need changing.

[gitstart-app[bot]]

Here is the GitStart Ticket for this issue: https://app.gitstart.com/clients/sourcegraph/tickets/SG-32671

[umpox]

@gitstart-sourcegraph Please take a look at this.

A good starting point would be to look at this initial PR for a while ago: https://github.com/sourcegraph/sourcegraph/pull/29620

We'll need to adapt it slightly and migrate it from Mocha to Jest.

EDIT: Hold slightly whilst we work out some points

[umpox]

@gitstart-sourcegraph Have unassigned this as there was some more investigation required that meant I focused on setting up the core foundation of the smoke tests.

Please close your linked issue too, we'll create new issues for additional work required in the smoke tests once the DevExp team start to integrate it with CI

[umpox]

Closed through https://github.com/sourcegraph/smoke-tests/tree/main/packages/web-functionality