add postgresql indexer

[Yongxuanzhang]

Postgress Indexer.

• Docker image running with a Dummy Executor -- get PostgreSQL Docker image and install Jina in it
• Executor performs CRUD ops
• Integration test.

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Benchmark

### indexing 100000 docs takes 1 minute and 4 seconds (64.40s)
### dumping 100000 docs takes 1 second (2.00s)
### dump path size: 112.35556 MBs
### reloading 100000 takes 3 seconds (3.16s)

NOTE: PSQL indexing can be optimized by inserting all in one go (for a future PR)

Compare w BinaryPb and Base here: jina-ai/jina#2307

[CatStark]

The work on postgresqldbhandler.py will mostly have to be re done after last conversation with Cristian but can serve as a base

[cristianmtr]

still some things to address