test: improve explore page tests

[SgtPooki]

address #2098 (comment)

clickFirstExploreChild is too naive for most tests, we need to test explicit CIDs

I am afraid this is too naive – for Apollo archives it hits the top level README.txt and never goes deeper than 1 lovel in:

🟢 http://localhost:3000/#/explore/QmSnuWmxptJZdLJpKRarxBMS2Ju2oANVrgbr2xWbie9b2D/README.txt
We have hardcoded CIDs of examples, we need to add more explicit test than parent dir.

Perhaps add a hardcoded, deterministic path that goes deep within directory tree, and then confirm it loaded the data with assert of expected info via testExploredCid ? This should be a good smoke-test.
No need to be inventive, just reuse paths marked as 🔴 and ℹ️ I mentioned (use the longest one, one test for dag-pb and dag-cbor each should be enough)
(not sure if needed, but in case you see test being slow/failing on CID) we can ipfs block get specific blocks that are used in tests as static test vectors into test directory, and ipfs block put them before running E2E tests, so they work in offline mode. (you can see which blocks are needed by manually traversing dag in IPLD Explorer and looking at block requests in Network tab in devtools)

This is being opened as a followup issue, because there was not much testing for the explore page to begin with, and significant tests have been added in #2098 that work well for what's already there.

This issue is intended to improve those tests even further.