Add snowflake lake loader support

[rlh1994]

Description

This PR in theory adds the ability to run snowflake on a lake loader external (iceberg) table. Currently it does not work because you can't write structured columns to a regular table, and dbt-snowflake doesn't yet support writing to iceberg. In theory it would work, but short of casting every single field within a context and unstruct to a varchar and back again, I am currently not able to test it.

I've worked around this similar to how we do in web with redshift not having a "* except" feature, by getting all columns from the CTE and then casting them all individually. This feels non-ideal, but at least in my basic testing does seem to allow the models to run at least.

I would suggest:

• Further testing to ensure everything is working as expected (test using

    snowplow__database: snowplow_dev1 
    snowplow__events_table: "EVENTS_ICEBERG" # Only set if not using 'events' table for Snowplow events data
    snowplow__enable_web: true
    snowplow__enable_mobile: false
    snowplow__backfill_limit_days: 1
    snowplow__start_date: '2024-06-13'
    snowplow__enable_yauaa: true
    snowplow__enable_ua: true

• If you do release this, announce limited support for it - for example thing such as passthrough fields and custom SQL in events this run may not work as expected.

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation Update
• 🎨 Style
• 🧑‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🤖 Build
• 🔁 CI
• 📦 Chore (Release)
• ⏩ Revert

Related Tickets & Documents

https://snplow.atlassian.net/browse/PE-6472

Checklist

• 💣 Is your change a breaking change?
• 📖 I have updated the CHANGELOG.md

Added tests?

• 👍 yes
• 🙅 no, because they aren't needed
• 🙋 no, because I need help

Added to documentation?

• 📓 internal package docs (ymls, macros, readme, if applicable)
• 📕 I have raised a Snowplow documentation PR if applicable (Link here)
• 🙅 no documentation needed

[optional] Are there any post-deployment tasks we need to perform?

[optional] What gif best describes this PR or how it makes you feel?

[agnessnowplow]

LGTM, considering the testing limitations and the method to convert the cases automatically, it "should" be ok. Keeping in mind the urgency I am fine to get this live with the caveat sentence in the release notes that it is still in a sort of POC state.