* Convert shell plugin to internal plugin

The purpose of this PR is to embed the shell plugin in the main dkron binary, that will facilitate creating a single binary with the most important executor, for easy deployment using a single binary.

* Remove debugging

* Release a light image tag

Omit all plugins except the shell plugin that will be included in the main binary.

* Upgrade react admin to v4

Co-authored-by: Victor Castell <victor@victorcastell.com>

* consul like approach: add server_lookup to make dkron independent from server node IP on raft layer
* handle memberupdate event
* query other servers before start & add test
* don't remove itself if node is a raft leader
* don't remove dkron server node if id matches

Config init was being done on the root level command but only the agent command was using config values.

Now config init is done as pre-run of agent command only, getting rid of extra messages in other commands when the config was missing.

Adapt fields to admin v4

http plugin is one of the most used plugins together with the shell plugin, embedding it in the main binary allow for more lean deployment.

* Tag v3

* Reuse http clients with the same configuration

…ed in general. (#1485)

Also add Pro protobuf and gen code as this should be public.

* minor improvement in rabbit mq executor

* fix flaky test