Converted generator into an ESM package, bumped yeoman-generator dependency to vision ^7.0.0

[sailingKieler]

As announced in the dev meeting yesterday - and although I don't see any urgency to merge it ASAP - here's my additional work on the generator:

• converted generator into an ESM package, bumped version of yeoman-generator to ^6.0.0

  • bumped typescript version to ~4.7.0 to be able to
    • set tsConfig options 'module' and 'moduleResolution' to value of 'Node16', see https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-7.html
    • deal with the transitive dependency 'mem-fs-editor' in version 10.0.x containing function alias assignments including type argument assignments, see https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-7.html#instantiation-expressions

• bumped version of 'yeoman-generator' to ^7.0.0

  • upgraded the dependency of 'yeoman-test' already to '^8.0.0' because of a problematic dependency in '^7.0.0' (mem-fs-editor@9.x...', has been by 'mem-fs-editor@10.y...')
  • added a 'resolution' on 'mem-fs@4.0.0', as that dependency is only referenced as peer-dependency by all up-to-date versions of using packages - which are not installed by yarn (in contrast to npm) -, but it's required at runtime; filed a request on Github to add 'mem-fs@4.0.0' as a prod dependency to 'yeoman-generator': yeoman-generator should declare an ordinary dependency on 'mem-fs' yeoman/generator#1495;
    besides 'yeoman-test@8.2.0' insists on 'mem-fs-editor@^10.0.3' (which depends on 'mem-fs@^3.0.0'), both declare "acceptDependencies" { "mem-fs": "^4.0.0" } - which again is not considered by yarn

[sailingKieler]

As indicated by the original title, I've prepared another change bumping to yeoman-generator@^7.0.0 (which took also quite notable time because of some nasty details).
However, some transitive dependency requires node 18, so I dropped that commit from this PR.
Will contribute it once #185 is merged.

[sailingKieler]

Since the ci build is now using Node18 (#193) I updated this branch and added my additional commit bumping the dependency of yeoman-generator to version 7.0.0.

[JonasHelming]

Cool, just to make sure: have you tested all templates whether they work as expected?