Whenever an unexpected error happens, the storage driver base client
will wrap it in a catch-all error, `storagedriver.Error`. Because of it,
if we get one of these errors we must extract the enclosed error before
trying to identify the best HTTP status for it, otherwise this will
always lead to a 500 Internal Server Error.

When deleting a manifest through the API, we 1) delete the manifest, 2)
obtain the list of tags (if any) that point to that manifest and 3)
delete them in a loop. If for some reason a tag is deleted between 2 and
3, the request will be halted with a 500 Internal Server error. This is
because we are not ignoring "path not found" errors during 3. This
change fixes that.

fix(api/errcode): extract enclosed error from a storage driver catch-all error

See merge request !759

fix(handlers): ignore tag not found errors when deleting a manifest

See merge request !760

So far these were being treated as unknown errors and therefore leading
to a 500 Internal Server Error response. For correctness, we should
propagate a status unavailable response from a service that we depend on
to serve a given request. This change is an attempt to fix that.

docs(storage): add note about mix/max values for the redirect expiry delay parameter

See merge request !761

fix(api/errcode): propagate 503 Service Unavailable status thrown by CGS

See merge request !763

fix(gc): always propagate correlation ID from agent to workers

See merge request !762

fix(gc/worker): delete task if dangling manifest no longer exists on database

See merge request !765

## [3.11.1](v3.11.0-gitlab...v3.11.1-gitlab) (2021-09-20)

### Bug Fixes

* **api/errcode:** extract enclosed error from a storage driver catch-all error ([800a15e2](800a15e2))
* **api/errcode:** propagate 503 Service Unavailable status thrown by CGS ([21041fef](21041fef))
* **gc:** always propagate correlation ID from agent to workers ([8de9c936](8de9c936))
* **gc/worker:** delete task if dangling manifest no longer exists on database ([dffdd72d](dffdd72d))
* **handlers:** ignore tag not found errors when deleting a manifest ([e7404169](e7404169))