Update etcd-client requirement from 0.8 to 0.9

Updates the requirements on [etcd-client](https://github.com/etcdv3/etcd-client) to permit the latest version.
- [Release notes](https://github.com/etcdv3/etcd-client/releases)
- [Commits](etcdv3/etcd-client@0.8.0...v0.9.0)

---
updated-dependencies:
- dependency-name: etcd-client
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

ballista/rust/scheduler/Cargo.toml

@@ -42,7 +42,7 @@ clap = { version = "3", features = ["derive", "cargo"] }
 configure_me = "0.4.0"
 datafusion = { path = "../../../datafusion/core", version = "7.0.0" }
 env_logger = "0.9"
-etcd-client = { version = "0.8", optional = true }
+etcd-client = { version = "0.9", optional = true }
 futures = "0.3"
 http = "0.2"
 http-body = "0.4"