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GH-38318: [Java][FlightRPC] Enable tests that leaked (#38719)

### Rationale for this change
This enables tests that are currently disabled to improve coverage and help others build tests based on these.

### What changes are included in this PR?
- Enable tests that were disabled due to flakey memory leaks
- Explicitly close child allocators in these tests to match
  the behavior of FlightServerTestRule which does not leak.
- Change TestBasicAuth to allocate only one server
- Change TestBasicAuth2 to allocate only one server and client
- Fix a bug in testBasucAuth2#asyncPut() not including credentials

### Are these changes tested?
Tested locally.

### Are there any user-facing changes?
No.
* Closes: #38318

Authored-by: James Duong <james.duong@improving.com>
Signed-off-by: David Li <li.davidm96@gmail.com>