[DPE-5587] Fix private IP resolution to use juju spaces

[phvalguima]

Up to this point OSD was taking the local IP (using the Python socket library) for the application endpoint.

However we need to use the IP published by Juju instead (Model.get_binding()) -- as this is the one that can be contacted externally.

The change has a impact on TLS certificates as well (as we are adjusting the IPs appearing in the certificate request accordingly).

Closes #121

[phvalguima]

The result of this PR:

• From src/core/models.py, on private_ip(), we can see the following IP: 10.10.10.186 -> full PDB https://pastebin.ubuntu.com/p/j4mgtrV5Rr/
• This is the /etc/hosts

Running the socket logic as we are doing currently on the charm indeed returns the wrong 127.0.1.1:

root@juju-865fea-0:/var/lib/juju/agents/unit-opensearch-dashboards-0/charm# python3 
Python 3.10.12 (main, Sep 11 2024, 15:47:36) [GCC 11.4.0] on linux                  
Type "help", "copyright", "credits" or "license" for more information.              
>>> import socket                                                                   
>>> socket.gethostbyname(socket.gethostname())                                      
'127.0.1.1'                                                                         
>>>                                                                                 

[Mehdi-Bendriss]

Thanks pedro, I have some questions.

[skourta]

LGTM. Left some minor questions.