style: forbid using console in mermaid src code

Adds an eslint rule forbidding using `console` in the mermaid source
code. Instead, the `src/logger` should be used instead, so that
websites can disable logging.

This is allowed in the `cypress/` and `demos/` folder.

I've also removed the two instances on `console.log`/`console.error`
that currently exist in the mermaid source code.

src/diagrams/git/gitGraphParserV2.spec.js

@@ -535,8 +535,6 @@ describe('when parsing a gitGraph', function () {
       testBranch3Merge,
     ] = Object.values(commits);
 
-    console.log(Object.keys(commits));
-
     expect(mainCommit.branch).toBe('main');
     expect(mainCommit.parents).toStrictEqual([]);