Support specifying Azure auth type

Currently the azure authentication flow seems to just pass off the auth options to the azidentity NewDefaultAzureCredential function: https://github.com/getsops/sops/blob/main/azkv/keysource.go#L232 While this does simplify things on sops side, that auth function does not allow fine grained control over what auth type is used. It is structured as a fall through but no ability to override, in my case managed identity and cli auth are populated so since managed identity will always be used even if I would like to use cli auth.

Can sops add some logic to be able to specify/disable certain auth types? (In my case to be able to disable managed identity, but the ability to generally control all auth types is probably ideal) I understand the simplicity of handing the auth flow off to the azure default auth flow, but a lot of control over the auth flow is lost in the process.

Start in azkv/keysource.go around line 232 and inspect how authentication options are passed to Azure's NewDefaultAzureCredential function. Trace the Azure key-source authentication flow to determine where auth-type controls belong. Done means users can specify or disable individual Azure authentication methods, including managed identity and CLI authentication.