[Enhancement]: remove mysql and redis dependencies from existing tests

[mdelapenya]

Proposal

I noticed that the docker_test.go file is consuming both mysql and redis/v8 dependencies.

We should avoid consuming service dependencies in the main module, and instead move them to an example module (see examples dir).

In the case of Redis, we merged a PR (#602) that is using a Dockerfile to test building images from a Dockerfile consuming a base Redis image living in a private registry. This is causing the import of redis client, as the test verifies that Redis is accesible from the test.

IMO the test should be simpler and should not use redis but a simple Nginx service and check that the default HTTP port is accessible, to name a straightly simple verification.

[mdelapenya]

We probably could close #659 after this is implemented

[mdelapenya]

Closing as resolved