Fix incompatibility for customers which implement HelixAdmin and BaseDataAccessor

Issues

[x] Fix incompatibility for customers which implement HelixAdmin and BaseDataAccessor

Description

After changing public interfaces, we did not add new default implementations for new methods. This is backwards incompatible. We are adding defaults in this PR that throw not implemented exception.

Tests

Changes that Break Backward Compatibility (Optional)

My PR contains changes that break backward compatibility or previous assumptions for certain methods or API. They include:

(Consider including all behavior changes for public methods or API. Also include these changes in merge description so that other developers are aware of these changes. This allows them to make relevant code changes in feature branches accounting for the new method/API behavior.)

Documentation (Optional)

In case of new functionality, my PR adds documentation in the following wiki page:

(Link the GitHub wiki you added)

Commits

My commits all reference appropriate Apache Helix GitHub issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
1. Subject is separated from body by a blank line
2. Subject is limited to 50 characters (not including Jira issue reference)
3. Subject does not end with a period
4. Subject uses the imperative mood ("add", not "adding")
5. Body wraps at 72 characters
6. Body explains "what" and "why", not "how"

Code Quality

My diff has been formatted using helix-style.xml (helix-style-intellij.xml if IntelliJ IDE is used)

apache / helix