Support auth through ydb-go-sdk in communication with YDB cluster

[kobzonega]

I hereby agree to the terms of the CLA available at: https://yandex.ru/legal/cla/?lang=en

Improve this Pull Request to support common types for authorization in communication with YDB cluster.

It is now possible to use field enable enforce_static_user_credentials: true in configuration YAML. YDB operator support 3 types of auth: anonymous (by default), access_token (oauth) and static credentials (username/password). Default password are using at init new cluster storage process if other not specified (just do not specify password field).

In general ydb-operator obtain a token from secretKeyRef from Storage spec.operatorConnection section and use that in following communication with YDB (for example in healthcheck and create tenant methods)

operatorConnection:
  accessToken:
    secretKeyRef:
      name: "mystorage-token"
      key: "token"
  staticCredentials:
    username: "root"
    password:
      secretKeyRef:
        name: "mystorage-root-password"
        key: "password"

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Not possible to specify enforce_static_user_credentials
Operator uses shell-in-pod-execution, raw grpc and ydb-go-sdk to communicate with YDB

Issue Number: YDBOPS-6056 (about static creds in general), YDBOPS-6646 (enforce_static_user_credentials fix), YDBOPS-7373 (support authorization common types for ydb-operator)

What is the new behavior?

• Now possible to specify enforce_static_user_credentials, operator correctly issues commands to YDB, using a token which it obtains from ydb-go-sdk. No raw grpc!
• Operator uses shell-in-pod-execution and ydb-go-sdk. Again, no raw grpc!

Other information

Refactoring:

• Reduced copypaste. internal/connection/connection.go is now the place for everything connected with communication. Later, other communication-specific logic can also be placed there.
• [minor] new method IsGrpcSecure to reduce the number of terribly long identical lines and copypaste. Will do the same later for Interconnect, I think.

[github-actions]

Hi! Thank you for contributing!
The tests on this PR will run after a maintainer adds an ok-to-test label to this PR manually. Thank you for your patience!