Add support for Azure US Government

Currently the azure-credentials-plugin and azure-keyvault-plugin do not support Azure US Government environment. Any try ends up with "AADSTS900382: Confidential Client is not supported in Cross Cloud" error.

The fix is required in the following plugins:

azure-credentials-plugin
azure-keyvault-plugin

Changes

Setting authorityHost on ClientSecretCredentialBuilder object. The authorityHost is taken from azureCredential.

Related issues

jenkinsci/azure-keyvault-plugin#66

Testing done

There is no automated test for this specific scenario.

Manual test

This change was manually tested with conjunction with fix for azure-keyvault-plugin.

Prerequisites

Azure US Government environment,
Azure Service Principal created,
Azure Key Vault created,
Azure Key Vault Sectet created,
azure-keyvaul-plugin with the fix https://github.com/jenkinsci/azure-keyvault-plugin/pull/207 installed.

Scenario

Add Azure Service Principal credential as GLOBAL, e.g. test-azure-us-gov-service-principal,
configure Azure Key Vault Plugin in Manage Jenkins => System:
- set Key Vault URL,
- set Credential ID to test-azure-us-gov-service-principal,
click Test Connection and make sure that there is no error and message like "Success, found (n) secrets in the vault" appeared,
make sure that the Azure Key Vault Secret has beed added to Jenkins Azure Credentials,

create testing Jenkins Pipeline which reads the secret, e.g.

    def secrets = [
        [ secretType: 'Secret', name: 'my-test-secret', envVariable: 'SECRET' ]
    ]
    withAzureKeyvault(secrets) {
        sh('echo ${SECRET}')
    }

run the pipeline and make sure the secret has been read.

### Submitter checklist
- [x] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [x] Ensure that the pull request title represents the desired changelog entry
- [x] Please describe what you did
- [x] Link to relevant issues in GitHub or Jira
- [x] Link to relevant pull requests, esp. upstream and downstream changes
- [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue

jenkinsci / azure-credentials-plugin