Add Docker images build instructions to the docs

[VJalili]

• Improve on gatk-sv docker images documentation;
• Update Docusaurus to its latest version (i.e., v. 2.4.1);
• Replace Docker-related figures with their mermaid-generated alternatives;
• Replace the git commit history example with its equivalent mermaid alternative;

Failed Python linting errors are unrelated to this PR, and not fixing them here to avoid triggering Docker image builds which are unrelated to this PR.

[mwalker174]

Thanks @VJalili, finally we can demystify our Docker system once and for all! Overall it looks ready, I just have a few questions and suggestions.