Update to eslint 9 and flat config

[ricellis]

PR summary

Update to eslint 9 and flat config

Fixes: i532

Note: An existing issue is required before opening a PR.

PR Checklist

Please make sure that your PR fulfills the following requirements:

• The commit message follows the
  Angular Commit Message Guidelines.
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

What is the current behavior?

Eslint 8 and .eslintrc.js

What is the new behavior?

Eslint 8 and eslint.config.mjs

Does this PR introduce a breaking change?

• Yes
• No

Other information

• Update lint packages
  • eslint to 9.x
  • plugins to latest versions
• Remove obsolete .eslintignore file (replaced by ignores in eslint.config.mjs)
• Remove obsolete eslintrc.js file (replaced by eslint.config.mjs
• Add .eslint-rules-ts.mjs for typescript modifications similar to .eslint-rules.json (these are currently in eslintrc.js but there are a lot, so having them in a file makes it a little easier to see what is going on in the new file.
• Make a few lint fixes
  • Long lines
  • A couple of comment based rule adjustments based on specific lines
  • Note changes in test/integration/cloudant.v1.test.js are made here so things can pass, but need matching generator changes that will be a no-op.

[mojito317]

Overall, this looks good, solid change. I just miss the explanatory comments that I worked on, so I would like to see those again, this might need a change in the extension of the typescript rules file.