Add projectDir argument to the configuration cache experiment github action

[ribafish]

Currently the experiment-config-cache expects to run the ./gradlew command in the root of the workflow. This means that any repository that has gradlew executable in a subdirectory can't use this github action.

I propose we add an optional projectDir argument, that would allow users to select the directory to run the configuration cache experiment from, same as we have for other experiments done via scripts - example: exp3.