admin api: rename EndpointHandler into RequestHandler to avoid confusion with RPC
wip: infrastructure for local api calls
admin api: fix things
admin api: first local endpoint to work with new scheme
admin api: implement SetWorkerVariable
**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#231Fix#295
Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: Deuxfleurs/garage#298
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>
