Allow client_id/client_secret authentication for Azure Key Vault and Trusted Signing

[spfeiffer-iem]

Azuresigntool allows authentication by access token or by client_id/client_secret. jsign only supports access token. This was briefly discussed as "nice improvement" in https://github.com/ebourg/jsign/issues/287

Obtaining an access token requires a web browser login (with 2FA in our case), while client_id/client_secret does not. For automated signing in CI pipelines using the latter would be much easier.

It would be very nice to have that functionality directly supported by jsign.

Thank you very much!