[FLINK-29593] Add QuantileSummary to help calculate approximate quant…

[jiangxin369]

…iles

What is the purpose of the change

Add QuantileSummary to help calculate approximate quantiles

Brief change log

• Add implementation of GK algorithm.
• Add merge operation to combine results of distributed datasets.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)

Documentation

• Does this pull request introduce a new feature? (yes )
• If yes, how is the feature documented? (JavaDocs)