Description

Now the original subscriptionModel has some problems:

1. The subscription logic for node is async, timely pull, and won't pull the inital value directly. This may cause plenty time, if a node's update frequency is low, the latency may be large to pull the first value.
2. In subscription model, one sample failure will cause permanent halt to the whole task.
3. And may be other problems.
   Thus, this PR rewrote the subscription logic, and changed the subscription value on push (with some performance optimization) to avoid "badWaitingForInitialData" after long term running.

This PR has:

• been self-reviewed.
  • concurrent read
  • concurrent write
  • concurrent read and write
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods.
• added or updated version, license, or notice information
• added comments explaining the "why" and the intent of the code wherever would not be obvious
  for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold
  for code coverage.
• added integration tests.
• been tested in a test IoTDB cluster.

Key changed/added classes (or packages if there are too many classes) in this PR