[FEATURE REQ] Managed Identity support for Backends

### Please describe the feature.

In the Azure Portal I configured my backend credentials using a Managed Identity like this:


When I extract the artifacts, the managed identity configuration is not included in the `backendInformation.json` file:
```json
{
"properties": {
"credentials": {
"header": {},
"query": {}
},
"protocol": "http",
"tls": {
"validateCertificateChain": true,
"validateCertificateName": true
},
"url": "https://test.com"
}
}
```

Would `credentials` be the place to store the managed identity properties?
For example:
```json
{
"properties": {
"credentials": {
"managedIdentity": {
"clientId":"my-managed-identity-client-id",
"resourceId":"api://example-scope", // I used the name from the portal as a property name, which makes sense for Azure resource backends (e.g. Service Bus, Key Vault, etc), but from an app reg OAuth perspective the name "scope" would be better suited in my opinion
},
},
"protocol": "http",
"tls": {
"validateCertificateChain": true,
"validateCertificateName": true
},
"url": "https://test.com"
}
}
```

I am open to contributing it myself if the maintainers find it a good idea and we can agree on the implementation details before I start developing.

Inizia tracciando come vengono estratti gli artefatti del backend e come backendInformation.json serializza le credenziali; nell’issue non sono identificati file sorgente né test. Confronta i campi di Azure Managed Identity mostrati nel portale con lo schema degli artefatti, concorda poi con i maintainer se usare resourceId o scope e verifica che la configurazione scelta sia inclusa negli artefatti estratti.

Scritto dal modello di indicizzazione a partire dal testo della issue.