[main < T279] Turn Docker into an optional dependency

[antepusic]

Description

This PR converts Docker from a dependency into an extra, on account of the docker package itself depending on the vulnerable pywin32 package.

Pull request type

• Build or packaging related changes

Related issues

Closes #261

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

######################################

Reviewer checklist (the reviewer checks this part)

• Core feature implementation
• Tests
• Code documentation
• Documentation on gqlalchemy/docs

######################################

[katarinasupe]

Looks okay. Update README and docs in new PR. I will generate new reference guide 😄