Refactor legal footer as React functional component (#8746)

I refactored the legal footer as React functional component in order to
clean up some technical debt.

I noticed two issues with the content, though:
- Amplitude was still being mentioned. I removed that in this PR
- Google Analaytics is still beinging mentioned. Should we remove that
as well?

### Steps to test:
- Go to http://localhost:9000/imprint
- Go to http://localhost:9000/legal

### Issues:
- Contributes to #8747

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(Please delete unneeded items, merge only when none are left open)
- [ ] Added changelog entry (create a `$PR_NUMBER.md` file in
`unreleased_changes` or use `./tools/create-changelog-entry.py`)
- [ ] Added migration guide entry if applicable (edit the same file as
for the changelog)
- [ ] Updated [documentation](../blob/master/docs) if applicable
- [ ] Adapted [wk-libs python
client](https://github.com/scalableminds/webknossos-libs/tree/master/webknossos/webknossos/client)
if relevant API parts change
- [ ] Removed dev-only changes like prints and application.conf edits
- [ ] Considered [common edge
cases](../blob/master/.github/common_edge_cases.md)
- [ ] Needs datastore update after deployment

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Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: hotzenklotz