[Improvement]: Introduce a way to run tests in a docker container

[azinneera]

Description

We have bal build --cloud but not bal test --cloud but to verify the package functionality in a cloud platform, we must run the tests also in a container. This applies to GraalVM verification as well. bal test --graalvm --cloud should run the tests in a container.

For this, there should be a standalone testable jar that can be run inside a container. We can check the possibility of generating a single testable jar or separate jars for each module.

[Dilhasha]

Following are the sub tasks for $subject.

• Create an uber jar for test modules
• Create test executable task and emit executable
• Verify code-coverage, mocking with the new test executable
• Lifecycle plugin implementation at C2C for running tests in docker container
• Support running tests in docker container when --graalvm --cloud
• Add test cases to cover above

[Dilhasha]

@Ramith-D-Rodrigo

Let's create a spreadsheet with all the cases we need to address

[Ramith-D-Rodrigo]

--graalvm --cloud=docker is supported now. Implemented using the testable fat jar while also considering the mocking features.

Added the relevant tests for the changes. --cloud flag changes are added in c2c repository. The tests added in this repo check the changes in BTestMain and the execution of testable fat jar.