Support multiple Key Vaults

[MT-Jacobs]

Feature description

Per the code, currently, only a single Key Vault can be connected to at once:

https://github.com/micronaut-projects/micronaut-azure/blob/a6924d9/azure-secret-manager/src/main/java/io/micronaut/azure/secretmanager/configuration/AzureKeyVaultConfigurationProperties.java#L27-L48

For most cases, this is great! However, it's possible to have cases where one key vault is used for environment-specific secrets and another is used for more common, shared secrets (think things like 3rd party API keys or auth configuration that might be shared by all nonprod environments, or other configuration that might be shared by several different applications).

Thinking on this, I'd imagine the biggest problem to solve here would involve resolving conflicts; if two Key Vaults have the same secret key, you probably need a way to signify which one takes precedence or otherwise nest the secrets under the key vault's base name.