feat: set sqlite pragma by env variable

[zzzming]

SQLite Pragma should not be hardcoded. This PR introduce an env variable to all these PRAGMA statement to be configurable without code changes.

To change the pragams you can set the env variable LANGFLOW_SQLITE_PRAGMAS using a JSON dict

The default value is unchanged and is

LANGFLOW_SQLITE_PRAGMAS="{"synchronous": "NORMAL", "journal_mode": "WAL"}"

[github-actions]

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_{Last Modified at 01 Aug 24 01:50 UTC}

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