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>

.github/dependabot.yml

@@ -78,3 +78,7 @@ updates:
     directory: "/crates/normalize-path"
     schedule:
       interval: "daily"
+  - package-ecosystem: "cargo"
+    directory: "/crates/simple-git"
+    schedule:
+      interval: "daily"

.github/workflows/release-pr.yml

@@ -23,6 +23,7 @@ on:
           - normalize-path
           - leon
           - leon-macros
+          - simple-git
       version:
         description: Version to release
         required: true