Configure structopt to report the right version

By default, structopt reports the value provided by
the env var CARGO_PKG_VERSION, feeded by Cargo when reading
Cargo.toml. However for Garage we use a versioning based on git,
so we often report a version that is behind the real version.
In this commit, we create garage_util::version::garage() that
reports the right version and configure all structopt subcommands
to call this function instead of using the env var.

src/util/Cargo.toml

@@ -24,6 +24,7 @@ hex = "0.4"
 tracing = "0.1.30"
 rand = "0.8"
 sha2 = "0.9"
+git-version = "0.3.4"
 
 chrono = "0.4"
 rmp-serde = "0.15"
@@ -43,5 +44,6 @@ hyper = "0.14"
 
 opentelemetry = { version = "0.17", features = [ "rt-tokio", "metrics", "trace" ] }
 
+
 [features]
 k2v = []

src/util/lib.rs

@@ -14,3 +14,4 @@ pub mod persister;
 pub mod time;
 pub mod token_bucket;
 pub mod tranquilizer;
+pub mod version;

src/util/version.rs

@@ -0,0 +1,7 @@
+pub fn garage() -> &'static str {
+	option_env!("GIT_VERSION").unwrap_or(git_version::git_version!(
+		prefix = "git:",
+		cargo_prefix = "cargo:",
+		fallback = "unknown"
+	))
+}