Add support for bounds in geohash_grid aggregation

[russcam]

Relates: #4341, elastic/elasticsearch#50002

This commit adds support for supplying bounds on a geohash_grid
aggregation, similar to how bounds are supplied on
geo_bounding_box query.

[Mpdreamz]

Unit test failure is unrelated

[xUnit.net 00:00:02.9411802]     Tests.Reproduce.TimeSpanSerialization.SerializeTimeSpansAsTicksAndStrings [FAIL]
  X Tests.Reproduce.TimeSpanSerialization.SerializeTimeSpansAsTicksAndStrings [152ms]
  Error Message:
   Expected 104d, 10h, 38m and 32s, but found 10d, 10h, 38m and 32s.
  Stack Trace:
     at FluentAssertions.Execution.XUnit2TestFramework.Throw(String message)
   at FluentAssertions.Execution.TestFrameworkProvider.Throw(String message)
   at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
   at FluentAssertions.Execution.AssertionScope.FailWith(Func`1 failReasonFunc)
   at FluentAssertions.Execution.AssertionScope.FailWith(String message, Object[] args)
   at FluentAssertions.Primitives.SimpleTimeSpanAssertions.Be(TimeSpan expected, String because, Object[] becauseArgs)
   at Tests.Reproduce.TimeSpanSerialization.SerializeTimeSpansAsTicksAndStrings() in /home/vsts/work/1/s/tests/Tests.Reproduce/TimeSpanSerialization.cs:line 30
[xUnit.net 00:00:03.2945958]     Tests.Reproduce.GithubPR3815.CanDeserializeNestedError [SKIP]
  ! Tests.Reproduce.GithubPR3815.CanDeserializeNestedError [1ms]

[Mpdreamz]

Opened #4423 to track the unit test failure