Bug 37917: Add some wait time to RecordSources_spec.ts for the intercepted request...

Bug 37917: Add some wait time to RecordSources_spec.ts for the intercepted request responses

This patch introduces the `cy.wait(500)` we use in several other Cypress
tests when an (intercepted) API request is made. This is very important
when tables are being rendered as DataTables is particularly bulky and
prone to take longer to finish loading the components if the CPU load is
a bit high.

I wasn't able to reproduce the problem very often, but you can test
yourself:

1. Run:
   $ ktd --shell
  k$ run_cypress --spec t/cypress/integration/Admin/RecordSources_spec.ts
2. Run it many times
=> FAIL: At some point it fails, you can overload your computer to try
3. Apply the patch
4. Repeat 2
=> SUCCESS: No failures :-D
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>