[AP-953] Add parquet support

[koszti]

Problem

Target-snowflake is using CSV files to load data from s3 into tables, but CSV is not the most efficient file format when loading into columnar tables.

Proposed changes

Add optional parquet support. To select between CSV and Parquet file format, create the file format snowflake object by one of the following SQLs:

To use CSV:

CREATE FILE FORMAT {database}.{schema}.{file_format_name}
TYPE = 'CSV' ESCAPE='\\' FIELD_OPTIONALLY_ENCLOSED_BY='"';

To use Parquet:

CREATE FILE FORMAT {database}.{schema}.{file_format_name} TYPE = 'PARQUET';

The required file format specific functions will be selected automatically. The code detects the file format type by running SHOW FILE FORMATS LIKE <file_format_name> SQL command

Key functions in the code:

• parquet.py: records_to_dataframe: Transforms a batch of singer record messages to pandas dataframe
• parquet.py: dataframe.to_parquet: Writes the DataFrame to the binary parquet format.
• parquet.py: create_merge_sql: Snowflake MERGE SQL generator for Parquet files
• csv.py: create_merge_sql: Snowflake MERGE SQL generator for CSV files.

Types of changes

What types of changes does your code introduce to PipelineWise?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

• Description above provides context of the change
• I have added tests that prove my fix is effective or that my feature works
• Unit tests for changes (not needed for documentation changes)
• CI checks pass with my changes
• Bumping version in setup.py is an individual PR and not mixed with feature or bugfix PRs
• Commit message/PR title starts with [AP-NNNN] (if applicable. AP-NNNN = JIRA ID)
• Branch name starts with AP-NNN (if applicable. AP-NNN = JIRA ID)
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions

[Samira-El]

I think there is a cleaner way of doing this. The factory design pattern is perfect to use here.

[koszti]

Addressed by 2cca9fe

and little shortening added by 42758b4

[Samira-El]

You can avoid having to duplicate c['name'] by doing '{0}=s.{0}'.format(c['name'])
`

[koszti]

addressed by 02bf2d0