docker-entrypoint tests

It's a simple environment to manually and locally test the changes in docker-entrypoint.sh.

Run tests

Update middleman.sh to reflect changes in docker-entrypoint.sh
Run ./tests/docker-entrypoint/caller.sh and ensure it prints the parameters in expected way.

Files

`script.sh`

Represents bump-everywhere.sh with same parameter parsing logic but just echoes the parameters
The test should assert that it takes and echoes the parameters in right way.

middleman.sh

Represents docker-entrypoint.sh that that's supposed to take the parameters from the caller and translates them into expanded parameters as the script would expect.
This is the system under test so update it to reflect changes in docker-entrypoint.sh

caller.sh

The entrypoint to run the test.
It calls the middleman as both:
- A user
  - Where parameter and values are sent in an expected way
  - E.g. --parameter value --parameter2 value2
- As GitHub actions
  - Each parameter name and value is double quoted together.
  - E.g. "--parameter value" "--parameter2 value2"