[16.0][ADD] base_external_system_odoorpc

[ntsirintanis]

This module adds an external system adapter for connecting to another Odoo instance
using the Python odoorpc client (JSON-RPC).

It is built on top of base_external_system and implements a new adapter model:

• external.system.odoo (System Type: External System RPC)

The adapter supports:

• Validating required connection parameters (host, port, database, username, password)
• Optional SSL transport (JSON-RPC over SSL)
• A context-managed client lifecycle via the base_external_system adapter contract
  (open client, perform calls, logout/cleanup)

[ntsirintanis]

@thomaspaulb @NL66278