tests: Skip testing deprecated non-async client methods in latest Elastic.Clients.Elasticsearch versions

[nr-ahemsath]

In the latest Elastic.Clients.Elasticsearch versions, non-async methods are deprecated. We previously ignored the deprecation warnings and continued testing these methods. This PR:

1. Uses preprocessor directives to avoid compiling the non-async methods in the latest ConsoleMF TFMs (net481 and net8.0), which are tied to the latest Elastic.Clients.Elasticsearch library versions.
2. Adds logic to the test code to skip testing the non-async methods for the latest version of Elastic.Clients.Elasticsearch
3. Modifies the Connect and GenerateError methods to be "async all the way" in order to use PingSync() instead of Ping() for those methods.

This also introduces the use of a 3rd-party library XUnit.SkippableFact to skip tests based on runtime conditions. I wanted to be explicit that we were skipping test cases rather than just having them pass without actually testing anything.

[tippmar-nr]

Looks good!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.86%. Comparing base (a6c4e74) to head (0eff085).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2569      +/-   ##
==========================================
+ Coverage   80.59%   80.86%   +0.26%     
==========================================
  Files         459      458       -1     
  Lines       28927    28985      +58     
  Branches     3177     3184       +7     
==========================================
+ Hits        23315    23439     +124     
+ Misses       4822     4756      -66     
  Partials      790      790              

Flag	Coverage Δ
Agent	81.78% <ø> (+0.29%)	⬆️
Profiler	72.59% <ø> (ø)

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see 169 files with indirect coverage changes