Relocate GoogleJsonClientFeature configurations closer to google-api-client [requires gax]

[mpeddada1]

Configurations related to google-api-client and google-http-client are currently present in gax-java. Libraries like java-datastore contain modules that bring in the google-api-client dependency but not gax so they aren't able to take advantage of these configs and as a result, have to add some of these configurations on their own. Reference: #928

[meredithslota]

@mpeddada1 Thank you for filing this — we have a proposal to refactor this library to use gax-java but it was tabled a few years ago because of bandwidth constraints. I will share it with you.

[mpeddada1]

Thank you for the reference @meredithslota!

[meredithslota]

FYI we are actively prioritizing this now, in combination with other efforts related to upgrading this library to use gax-java (cc: @jainsahab and @kolea2).