Upgrade okhttp and regrofit dependencies to use at least okhttp3 version 4.2.0

[ausykaso]

Problem:

• The Contentful SDK's are using deprecated versions of

  <retrofit.version>2.5.0</retrofit.version>
  <okhttp.version>3.12.12</okhttp.version>
  

• That forces a version clash when used together with other dependencies that use okhttp3 4.2.x versions (i.e. Voucherify SDK, see Issue #104).

Expected behavior:

• Contentful SDK's (including CMA) are working with the current okhttp3 versions, at least 4.2.0.

[ausykaso]

Unfortunately there's no answer or reaction. Seems that there's no interest to think about the usage of uptodate dependencies. This will lead us to recomend our customer, not to prefer the usage of that SDK or otherwise to use a patched fork.