Refactor: Extract new crate simple-git (#1304)

`binstalk-downloader` contains stuff about http(s) before the
git code is moved into it and now it becomes http and git.

While git indeed uses http stuff, which is why I decided to put
it into binstalk-downloader, it is more than just downloading
since it is stateful (can be cached locally and updated)
where as http is stateless.

Also `binstalk-downloader`'s codegen time now increases
dramatically and it also creates extra dependencies for
binstalk-fetchers, delaying its execution.

The git code also don't use anything from `binstalk-downloader`
at all, it makes sense to be an independent crate.

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

Cargo.lock

@@ -260,6 +260,7 @@ dependencies = [
  "maybe-owned",
  "miette",
  "semver",
+ "simple-git",
  "strum",
  "target-lexicon",
  "tempfile",
@@ -295,11 +296,9 @@ dependencies = [
  "bytes",
  "bzip2",
  "compact_str",
- "derive_destructure2",
  "flate2",
  "futures-util",
  "generic-array",
- "gix",
  "httpdate",
  "percent-encoding",
  "quinn 0.10.2",
@@ -379,6 +378,7 @@ dependencies = [
  "serde",
  "serde_json",
  "sha2",
+ "simple-git",
  "tempfile",
  "thiserror",
  "tokio",
@@ -3392,6 +3392,18 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "simple-git"
+version = "0.0.0"
+dependencies = [
+ "compact_str",
+ "derive_destructure2",
+ "gix",
+ "thiserror",
+ "tokio",
+ "tracing",
+]
+
 [[package]]
 name = "slab"
 version = "0.4.8"