config: support {{ replicaset_name }} and {{ group_name }}

[TarantoolBot]

The declarative configuration supports {{ instance_name }} template
variable from the beginning.

Now, two more ones were added: {{ replicaset_name }} and
{{ group_name }}.

All the template variables are set according to the
instance/replicaset/group topology from the given configuration.

Example:

console:
  socket: '{{ group_name }}/{{ replicaset_name }}/{{ instance_name }}.admin'

groups:
  g:
    replicasets:
      r:
        instances:
          i: {}

The admin console will be at g/r/i.admin for instance i.

Requested by @Totktonada in tarantool/tarantool@f059973.

[andreyaksenov]

https://docs.d.tarantool.io/en/doc/3.0/concepts/configuration/#predefined-variables