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/put.rs

@@ -19,7 +19,7 @@ use garage_model::s3::block_ref_table::*;
 use garage_model::s3::object_table::*;
 use garage_model::s3::version_table::*;
 
-use crate::error::*;
+use crate::s3::error::*;
 use crate::s3::xml as s3_xml;
 use crate::signature::verify_signed_content;
 
@@ -183,8 +183,8 @@ fn ensure_checksum_matches(
 ) -> Result<(), Error> {
 	if let Some(expected_sha256) = content_sha256 {
 		if expected_sha256 != data_sha256sum {
-			return Err(Error::BadRequest(
-				"Unable to validate x-amz-content-sha256".to_string(),
+			return Err(Error::bad_request(
+				"Unable to validate x-amz-content-sha256",
 			));
 		} else {
 			trace!("Successfully validated x-amz-content-sha256");
@@ -192,9 +192,7 @@ fn ensure_checksum_matches(
 	}
 	if let Some(expected_md5) = content_md5 {
 		if expected_md5.trim_matches('"') != base64::encode(data_md5sum) {
-			return Err(Error::BadRequest(
-				"Unable to validate content-md5".to_string(),
-			));
+			return Err(Error::bad_request("Unable to validate content-md5"));
 		} else {
 			trace!("Successfully validated content-md5");
 		}
@@ -428,7 +426,7 @@ pub async fn handle_put_part(
 	// Check part hasn't already been uploaded
 	if let Some(v) = version {
 		if v.has_part_number(part_number) {
-			return Err(Error::BadRequest(format!(
+			return Err(Error::bad_request(format!(
 				"Part number {} has already been uploaded",
 				part_number
 			)));
@@ -513,7 +511,7 @@ pub async fn handle_complete_multipart_upload(
 
 	let version = version.ok_or(Error::NoSuchKey)?;
 	if version.blocks.is_empty() {
-		return Err(Error::BadRequest("No data was uploaded".to_string()));
+		return Err(Error::bad_request("No data was uploaded"));
 	}
 
 	let headers = match object_version.state {
@@ -574,8 +572,8 @@ pub async fn handle_complete_multipart_upload(
 		.map(|x| x.part_number)
 		.eq(block_parts.into_iter());
 	if !same_parts {
-		return Err(Error::BadRequest(
-			"Part numbers in block list and part list do not match. This can happen if a part was partially uploaded. Please abort the multipart upload and try again.".into(),
+		return Err(Error::bad_request(
+			"Part numbers in block list and part list do not match. This can happen if a part was partially uploaded. Please abort the multipart upload and try again."
 		));
 	}