Adds Support for COPY TO/FROM Google Cloud Storage

[aykut-bozkurt]

Supports following Google Cloud Storage uri forms:

• gs:// <bucket> / <path>

Configuration

The simplest way to configure object storage is by creating a json config file like [/tmp/gcs.json]:

$ cat /tmp/gcs.json
{
  "gcs_base_url": "gs://testbucket/test.parquet",
  "disable_oauth": false,
  "client_email": "...",
  "private_key_id": "...",
  "private_key": "..."
}

Alternatively, you can use the following environment variables when starting postgres to configure the Google Cloud Storage client:

• GOOGLE_SERVICE_ACCOUNT_KEY: json serialized service account key
• GOOGLE_SERVICE_ACCOUNT_PATH: an alternative location for the config file

Closes #62

[codecov]

Codecov Report

Attention: Patch coverage is 95.55556% with 6 lines in your changes missing coverage. Please review.

Project coverage is 91.93%. Comparing base (3ff46d5) to head (ec5c082).

Files with missing lines	Patch %	Lines
src/object_store/gcs.rs	86.84%	5 Missing ⚠️
src/object_store/object_store_cache.rs	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
+ Coverage   91.88%   91.93%   +0.04%     
==========================================
  Files          77       78       +1     
  Lines       10320    10444     +124     
==========================================
+ Hits         9483     9602     +119     
- Misses        837      842       +5     

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