improve internal item counter mechanisms and implement bucket quotas (#326)

- [x] Refactoring of internal counting API
- [x] Repair procedure for counters (it's an offline procedure!!!)
- [x] New counter for objects in buckets
- [x] Add quotas to buckets struct
- [x] Add CLI to manage bucket quotas
- [x] Add admin API to manage bucket quotas
- [x] Apply quotas by adding checks on put operations
- [x] Proof-read

Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/326
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>

Cargo.lock

@@ -387,6 +387,12 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "bytesize"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c58ec36aac5066d5ca17df51b3e70279f5670a72102f5752cb7e7c856adfc70"
+
 [[package]]
 name = "cc"
 version = "1.0.73"
@@ -948,6 +954,7 @@ dependencies = [
  "aws-sdk-s3",
  "base64",
  "bytes 1.1.0",
+ "bytesize",
  "chrono",
  "futures",
  "futures-util",