Restructure Docs for Docker Compose

[etrandafir93]

Restructure documentation for the Docker Compose module, focusing on:

• focus on ComposeContainer instead of DockerComposeContainer as the primary source of examples. (current doc uses DockerComposeContainer in the majority of the code snippets)

• keep the code samples independent from the JUnit execution (the code examples include JUnit4's @ClassRule)

• use MkDocsfor the code snippets wherever possible (currently, the code samples are written as code blocks in markdown, instead of using MkDocs)

• add links to Javadoc and to other documentation pages wherever possible

Page to be modified: https://java.testcontainers.org/modules/docker_compose/

[etrandafir93]

@eddumelendez, when you have a few minutes, can you please let me know if I can help with anything else here? - cheers :)