Add backtrace feature to anyhow

Improved backtrace support for errors in Rust is currently in progress:
rust-lang/rust#53487. Adding the feature lets
anyhow add backtraces already which greatly improves readability of
errors in tests.

Cargo.toml

@@ -15,7 +15,7 @@ postgres = { version = "0.19.2", features = ["with-serde_json-1"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 typetag = "0.1.7"
-anyhow = "1.0.44"
+anyhow = { version = "1.0.44", features = ["backtrace"] }
 clap = { version = "3.0.0", features = ["derive"] }
 toml = "0.5"
 version = "3.0.0"