feat(tvix/store): add xp-store-composition-cli feature flag

This can be used to transitively enable the `xp-composition-cli` feature
flag in the `tvix-store` crate, which is unnecessarily hard to do with
crate2nix.

Change-Id: I3f7c505a3fd505561c9a7b2f063b6540532cdfd4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12809
Tested-by: BuildkiteCI
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>

tvix/nar-bridge/Cargo.toml

@@ -39,6 +39,7 @@ tonic-build = { workspace = true }
 [features]
 default = ["otlp"]
 otlp = ["tvix-tracing/otlp"]
+xp-store-composition-cli = ["tvix-store/xp-composition-cli"]
 
 [dev-dependencies]
 hex-literal = { workspace = true }