refactor!: move to axum

[simonsan]

Fixes #2
Fixes #23

TODO:

• Fix error handling
• Check unit/integration tests
• add e2e test cases using restic(e.g. https://github.com/rustic-rs/rustic/blob/8afcd3ee999e634f24c420ec76fd612ee89d45c9/.github/workflows/compat.yml ) to make sure, we are compatible with the rest implementation
• use typed routing (revert changes from PR Feature/axum #45 )

[simonsan]

It may make sense to factor out the tests and merge them first, when they run through also with the old code. Or make them run with the old code.

[simonsan]

When merging this PR:

• deactivate the nightly builds for the time being, so this version is not being delivered until stabilized

• create a note in the Readme, that this version is currently unstable and should not be used outside a development context.

[simonsan]

Let's merge this and work in another PR to get the typed_routing going and implement more tests.