patch: update terraform modules for replica set and sharded cluster

[patriciareinoso]

Description

This PR updates the terraform modules
The replica set is a charm module. Variables, outputs and file name were changed according to CC008 and DA219

The charm sharded TF module became a product module according to the spec and it now imports mongos TF module

Notable changes

• Extract the terraform linting into a tox env
• Update the juju provider to ~>2.0
• New format for the outputs
• Not all the applications are deployed, we keep data-integrator, s3-integrator (optional), gcs-integrator (optional)
• New way of declaring integrations: use a variable. This allows to make same-model relations or cross-model relations

Example

Modules are still under development so for now no version release