Implement support for ServiceAccount auth

[the-avant-it]

Currently you can only use Metadata and OAuth token for auth. Metadata is not applicable for all use cases since it requires your service to run on Yandex Cloud, but OAuth gets expired after one year with is not good also. So service account auth option since it has no expiration problem and not coupled to YC's infrastructure

[the-avant-it]

May be, for now, there is way I can request new oauth token to renew it from code automatically?

[nikolaymatrosov]

Please avoid using OAuth tokens for any type of automation. Instead, it's recommended to utilize a service account with an authorized key. Here are a few approaches to consider:

1. Implement your own ICredentialsProvider to exchange a JWT token, signed by the authorized private key, for access.
2. Use a third-party package that provides this functionality, such as YandexCloud.IamJwtCredentials.
3. Alternatively, you may wait for the merge of pull request Support authorized key #27, which will add this functionality to the SDK.

These methods ensure secure and efficient authorization for automated processes.

[the-avant-it]

Use a third-party package that provides this functionality, such as YandexCloud.IamJwtCredentials.

Looks like what I need, thank you!