build: strip release binaries

This significantly reduces binary size for deltachat-rpc-server,
from 42 MiB to 15 MiB in case of aarch64.

Cargo.toml

@@ -24,6 +24,7 @@ lto = true
 panic = 'abort'
 opt-level = "z"
 codegen-units = 1
+strip = true
 
 [patch.crates-io]
 quinn-udp = { git = "https://github.com/quinn-rs/quinn", branch="main" }