Upgrade tuf dependency to 5.0.0

[dennisvang]

Need to upgrade to python-tuf version 5.0.0, which was released recently.

This introduces some breaking changes, as mentioned in the tuf changelog:

This release, most notably, marks stable securesystemslib v1.0.0 as minimum requirement. The update causes a minor break in the new DSSE API (see below) and affects users who also directly depend on securesystemslib. See the securesystemslib release notes and the updated python-tuf examples (#2617) for details. ngclient API remains backwards-compatible.

Note that securesystemslib 1.0.0 introduces several major changes. For example, the interface module has been removed, so we need to adapt to the new crypto signer api.