feat: Allows to choose Terraform version for Acceptance Tests, default to latest version (#1684)

* move CI

* remove PARALLEL_GO_TEST and use default value

* remove ACCTEST_TIMEOUT and use default value

* move TF_LOG

* move TF_ACC

* move SKIP_TEST_EXTERNAL_CREDENTIALS

* allow to pass tf version or use latest

* remove release leftovers

* also run migration tests nightly

* allow to pass TF version in migration tests

* extract common vars in migration tests

* use vars for ACCESS_TIMEOUT and TF_LOG

Author: lantoli