Update release testing section of website to reference standalone-capable ITs

"I have no issue with the code changes by themselves, but I wonder if this is the best place for them. IMO, this functionality will not be remembered when it comes time to perform release testing as I think the majority of testing occurs from the accumulo-testing repo. If this is merged, then I would suggest that the [release testing](https://accumulo.apache.org/contributor/verifying-release#testing-basics) section of the website be updated to reference this test and any other standalone-capable ITs.

I did a quick look in the test module, and it looks like the following classes may work in a standalone capacity:

TestIngest
TestMultiTableIngest
VerifyIngest
TestRandomDeletes

These classes aren't tests, but utilities that ITs use."

_Originally posted by @dlmarion in https://github.com/apache/accumulo/pull/4051#pullrequestreview-3718434986_

Start with the website's release testing section at contributor/verifying-release#testing-basics and review the standalone-capable classes listed in the issue: TestIngest, TestMultiTableIngest, VerifyIngest, and TestRandomDeletes. Update the section to reference the applicable tests, and consider the change complete when release testers can find these standalone-capable ITs from the documentation.

Written by the indexing model from the issue text.