iotdb [IoTDB-804] Index Framework Part 2: Core

Description

This pull request is about the index framework, aiming at enabling IoTDB to support similar research and other index types. We appreciate all comments and suggestions. Thanks to all reviewers.

It is the second part of the index framework, which is about the core codes of the framework and interfaces for index developers.

The design document (temporarily in Chinese) can be viewed in the project docs (docs/zh/SystemDesign/Index/Index.md) or website
The previous part is at PR-2024
The issue is at JIRA-804.

This PR has:

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

Key changed/added classes

Most codes are under the package org.apache.iotdb.db.index:

The framework codes: IndexManager and others
A brief query code: package read
The interface of the feature extractor: feature.IndexFeatureExtractor
The index interface opened for the index developers and researchers algorithm.IoTDBIndex and a demo implementation algorithm.NoIndex
Related UT and IT.

The implementation of FeatureExtractor and IoTDBIndex (the whole-matching index RTree+PAA and the subsequence matching index ELB) will be submitted in the third part (the last part). We appreciate more other index integration.

Interactions with Other Modules

Start: be called in RegisterManager#register
Create/Drop Index: be called in PlanExecutor#createIndex and PlanExecutor#dropIndex
Insert: so far, the index insertion will only be called in MemTableFlushTask
Query: be called in QueryIndexExecutor#executeIndexQuery.