[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.

Beginne damit nachzuverfolgen, wie Backend-Artefakte extrahiert werden und wie backendInformation.json Anmeldedaten serialisiert; im Issue sind keine Quelldateien oder Tests angegeben. Vergleiche die im Portal angezeigten Felder der Azure Managed Identity mit dem Artefaktschema, stimme dich dann mit den Maintainers über resourceId gegenüber scope ab und verifiziere, dass die gewählte Konfiguration in den extrahierten Artefakten enthalten ist.

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