* pre-create directories for mounting and use /spring/cloud-contract and /contract and /spring-cloud-contract
* add documentation on how to run a customized gradle build to create tests
As part of 4d7110 Docker base images were updated to ubuntu:21.04.
According to #gh-1579 the intention is to update to Ubuntu LTS version.
21.04 is not LTS version and as a matter of fact it is not yet released
version.
Change the docker base image to the the intended version 20.04 LTS.
* Rewritting to java
- rewritten a lot of Spring Cloud Contract Spec module to Java
- extracted all Groovy stuff to a separate package
- will now continue writing extension modules
- spring-cloud-contract-spec will be written purely in java
- spring-cloud-contract-spec-groovy will have Groovy extensions
fixes gh-1130
with this change we're adding generation of 2 docker images - verifier and stub runner
we also added a project `spring-cloud-contract-stub-runner-boot` which contains a far jar with stub runner boot
fixes gh-526, gh-516
