Use zstd without dynamic linking due to musl usage (#19627)

Due to leaning towards `musl` builds, unit features for `zstd` and link
it statically too for Zed.


https://github.com/gyscos/zstd-rs/blob/bfe1e34f593c2427e9dc35f1b98d06788174711f/zstd-safe/zstd-sys/build.rs#L260
shows that `ZSTD_SYS_USE_PKG_CONFIG` env var can be used to return this
behavior.

Release Notes:

- N/A