Initial Snowflake migration docs

[justindeguzman]

This is a simplified doc of the migration section from this blog post:
https://clickhouse.com/blog/clickhouse-vs-snowflake-for-real-time-analytics-comparison-migration-guide#migrating-data

[robot-clickhouse]

This is an automated comment for commit f659664 with description of existing statuses. It's updated for the latest CI running

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[kellytoole]

This looks great! Thank you so much again

[tbragin]

@gingerwizard any reviews? what are the next steps here? cc @Ryado

[gingerwizard]

last time i checked they do export OBJECT as JSON string..this is subject to change. i raised a question and they planned to possibly change. Maybe add note?

[gingerwizard]

note subject to change

[gingerwizard]

LGTM. Maybe note the string export of JSON is subject to change and users should do a DESCRIBE s3() toi check the schema

[justindeguzman]

LGTM. Maybe note the string export of JSON is subject to change and users should do a DESCRIBE s3() toi check the schema

Just to keep it simple, I don't think we should add this info unless Snowflake's behavior actually changes.

Thanks for reviewing @gingerwizard!