First version of admin API (#298)

**Spec:**

- [x] Start writing
- [x] Specify all layout endpoints
- [x] Specify all endpoints for operations on keys
- [x] Specify all endpoints for operations on key/bucket permissions
- [x] Specify all endpoints for operations on buckets
- [x] Specify all endpoints for operations on bucket aliases

View rendered spec at <https://git.deuxfleurs.fr/Deuxfleurs/garage/src/branch/admin-api/doc/drafts/admin-api.md>

**Code:**

- [x] Refactor code for admin api to use common api code that was created for K2V

**General endpoints:**

- [x] Metrics
- [x] GetClusterStatus
- [x] ConnectClusterNodes
- [x] GetClusterLayout
- [x] UpdateClusterLayout
- [x] ApplyClusterLayout
- [x] RevertClusterLayout

**Key-related endpoints:**

- [x] ListKeys
- [x] CreateKey
- [x] ImportKey
- [x] GetKeyInfo
- [x] UpdateKey
- [x] DeleteKey

**Bucket-related endpoints:**

- [x] ListBuckets
- [x] CreateBucket
- [x] GetBucketInfo
- [x] DeleteBucket
- [x] PutBucketWebsite
- [x] DeleteBucketWebsite

**Operations on key/bucket permissions:**

- [x] BucketAllowKey
- [x] BucketDenyKey

**Operations on bucket aliases:**

- [x] GlobalAliasBucket
- [x] GlobalUnaliasBucket
- [x] LocalAliasBucket
- [x] LocalUnaliasBucket

**And also:**

- [x] Separate error type for the admin API (this PR includes a quite big refactoring of error handling)
- [x] Add management of website access
- [ ] Check that nothing is missing wrt what can be done using the CLI
- [ ] Improve formatting of the spec
- [x] Make sure everyone is cool with the API design

Fix #231
Fix #295

Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/298
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>

src/api/s3/get.rs

@@ -17,7 +17,7 @@ use garage_model::garage::Garage;
 use garage_model::s3::object_table::*;
 use garage_model::s3::version_table::*;
 
-use crate::error::*;
+use crate::s3::error::*;
 
 const X_AMZ_MP_PARTS_COUNT: &str = "x-amz-mp-parts-count";
 
@@ -210,8 +210,8 @@ pub async fn handle_get(
 
 	match (part_number, parse_range_header(req, last_v_meta.size)?) {
 		(Some(_), Some(_)) => {
-			return Err(Error::BadRequest(
-				"Cannot specify both partNumber and Range header".into(),
+			return Err(Error::bad_request(
+				"Cannot specify both partNumber and Range header",
 			));
 		}
 		(Some(pn), None) => {
@@ -302,9 +302,9 @@ async fn handle_get_range(
 				let body: Body = Body::from(bytes[begin as usize..end as usize].to_vec());
 				Ok(resp_builder.body(body)?)
 			} else {
-				None.ok_or_internal_error(
+				Err(Error::internal_error(
 					"Requested range not present in inline bytes when it should have been",
-				)
+				))
 			}
 		}
 		ObjectVersionData::FirstBlock(_meta, _first_block_hash) => {