[3.19] community/arti: upgrade to 1.2.3
- run riscv64 tests with RUST_BACKTRACE=1 (riscv64 currently disabled)
- build with --features=full --package arti
- add OnionService.md to -doc subpackage
cherry-picked !65582 (merged)
https://gitlab.torproject.org/tpo/core/arti/-/blob/arti-v1.2.3/CHANGELOG.md
this is not a security upgrade, as we never had 1.2.2, it's a feature and bugfix upgrade