Snowpark-extensions

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- unpinning snowpark dependency
- removing deprecated functionality already provided in snowpark

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- updating snowpark dependency to latest 1.15.0
- removed functions that are already present in snowpark library

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- updating snowpark dependency to latests 1.14.0
- deprecating to_utc_timestamp as it is now natively supported
- added fromJson extensions for StructType and StructField

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- updating snowpark dependency to latests 1.11.1

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- fixing issue with the `%%sql` magics that was causing a double execution
- update README.md for PMML
- update for the `extras/wheel_loader` thanks Karol Tarcak

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- added functions.to_utc_timestamp extension