Creating a self-signed certificate for "Organizzazione fittizia per il collaudo"

**Describe the bug**

I'm trying to create a certificate for "Organizzazione fittizia per il collaudo", but the IPA code "__aggrsint" does not exist on indicepa.gov.it and I can not go ahead with the creation.

**To Reproduce**

Steps to reproduce the behavior:
1. Execute the follow command: spid-compliant-certificates generator --key-size 2048 --days 365 --entity-id https://blabla.it/pub-ag-lite/TEST --common-name 'Organizzazione fittizia per il collaudo' --locality-name Roma --org-id PA:IT-__aggrsint --org-name 'Organizzazione fittizia per il collaudo' --sector public

**Expected behavior**

Expects me to create the certificate for testing purposes

**Screenshots**


**Environment (please complete the following information):**

- OS: Windows 10

**Additional context**

The company I work for is going to be federate as public aggregator, for that I need to use --sector public on the command above

Start by reproducing the `spid-compliant-certificates generator` command shown in the issue and inspect how `--sector public` validates the `--org-id` value. Confirm whether the requested test certificate can be generated for the missing `__aggrsint` IPA code, then document or test the resulting behavior.

Written by the indexing model from the issue text.