test(pf5): fix broken tests after PF5 upgrades

[tthvo]

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Related to #1303

Description of the change:

Unit/Integration tests

Fixed broken tests after upgrading to Patternfly 5. This PR involves the following changes to the tests:

• Updated snapshots. Some requires mocking ref (See below notes).
• Corrected the display texts or aria-label texts that the tests use for locating the elements.
• Wrapped codes that cause React state changes in act where applicable, for example, actions that opens modal.
• Added/Removed tests to accommodate new designs, for example, label editor or range filters.

I also added some tips/notes (i.e. TESTING.md) that I figured out when fixing the tests.

Other bug fixes

Thanks to the unit tests, the following bugs are fixed:

• Fixed bug where in bulk label editor, if a label input is invalid, all labels after that is removed. Only the invalid one should be removed.
• Fixed agent template row action. This was missed in previous PRs.
• Use SearchInput for agent template search bar (i.e. has Search icon for consistency).

Notes

There are some odd instances where snapshot test environment messes up DOM testing with react-testing-library. For example, createNodeMock (only for snapshot rendering) is leaked into other DOM tests.

Reordering the snapshot tests to last solved the problem. We might need some restructuring in #661 to split the 2 types of unit tests.

[tthvo]

Pheww! I think the tests are all updated to accommodate the PF5 upgrades now :D

Not satisfied with it though, as many test logics are not yet standardized (i.e. repeated or done differently). I hope there will be some time to get to #848 to clean things up :D

And many thanks again to @maxcao13 for helping out with this work!!!

[andrewazores]

I'll start reviewing this now, but it might take a bit of time :-)