Update Typescript to v4.8

[hotzenklotz]

While updating the immutability-helpers (PR #6565), I had a look at the latest Typescript version 4.8. According to their release notes, there might be some speedups for the compile and watch tasks and better type understanding in some situations. :-)
In our code base it only resolved 2 ignored/suppressed type errors.

Full release notes: https://devblogs.microsoft.com/typescript/announcing-typescript-4-8/

While at it, I had to update ESLint to a compatible version. I bumped some of the eslint rules as well. I dropped the ts-migrate package since we are not using it anymore.

Steps to test:

• CI should be enough

Issues:

• None

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(Please delete unneeded items, merge only when none are left open)

• Updated (unreleased) changelog
• Updated (unreleased) migration guide if applicable
• Updated documentation if applicable
• Adapted wk-connect if datastore API changes
• Adapted wk-libs python client if relevant API parts change
• Needs datastore update after deployment
• Ready for review

[philippotto]

🚀