* Daemon: support remote configuration
This:
* Adds support for fetching the configuration from a remote HTTP location:
`ipfs-cluster-service init http://localhost:8080/ipfs/Qm...` will instruct
cluster to read the configuration file from ipfs on start (potentially making
use of ipns and dnslink).
This is done by creating a `service.json` like `{ "source": <url> }`.
The source is then read when loading that configuration every time the daemon starts.
This allows to let users always use a mutating remote configuration, potentially
adding/removing trusted peers from the list or adjusting other things.
* Configuration and state helpers from ipfs-cluster-service have been extracted
to its own cmdutils package. This will help supporting something like an
`ipfs-cluster-follow` command in the next releases.
* Allows to disable the rest api by not defining it in the configuration (I thought
this was already so, but apparently only affected the ipfsproxy).
* Removes informer/allocator configurations from the daemon (--alloc). No one used
a non default pair. In fact, it was potentially buggy to use the reposize one.
This adds a new "crdt" consensus component using go-ds-crdt.
This implies several refactors to fully make cluster consensus-component
independent:
* Delete mapstate and fully adopt dsstate (after people have migrated).
* Return errors from state methods rather than ignoring them.
* Add a new "datastore" modules so that we can configure datastores in the
main configuration like other components.
* Let the consensus components fully define the "state.State". Thus, they do
not receive the state, they receive the storage where we put the state (a
go-datastore).
* Allow to customize how the monitor component obtains Peers() (the current
peerset), including avoiding using the current peerset. At the moment the
crdt consensus uses the monitoring component to define the current peerset.
Therefore the monitor component cannot rely on the consensus component to
produce a peerset.
* Re-factor/re-implementation of "ipfs-cluster-service state"
operations. Includes the dissapearance of the "migrate" one.
The CRDT consensus component defines creates a crdt-datastore (with ipfs-lite)
and uses it to intitialize a dssate. Thus the crdt-store is elegantly
wrapped. Any modifications to the state get automatically replicated to other
peers. We store all the CRDT DAG blocks in the local datastore.
The consensus components only expose a ReadOnly state, as any modifications to
the shared state should happen through them.
DHT and PubSub facilities must now be created outside of Cluster and passed in
so they can be re-used by different components.
