docs: DOC-655: Groovy SQL how-to & reference

[elijahpetty]

https://deephaven.atlassian.net/jira/software/projects/DOC/boards/8?selectedIssue=DOC-655

[github-actions]

Deploying docs previews for 55125c9 (available for 14 days)

Groovy

[jjbrosnan]

Only two minor comments. Here's a larger comment, though:

This PR adds one user guide, named identically to the Python user guide. However, this Groovy page differs immensely from the Python page because the SQL integration is much more fleshed out in Groovy/Java.

I looked through the source code for the Python SQL integration and it appears that, unlike most of our Python API, it's not just Java wrapped in Python.

This comment is long and there may be nothing to actually do as a result of it, but the overarching comment is that in Python you can actually query databases like Postgres into DH tables. This guide only runs SQL queries against DH tables to get new DH tables. If you can do in Groovy what you can do in Python, we also need to document that.

[jjbrosnan]

Is it better to list what you can do instead of what you can't do? The list below seems pretty comprehensive.

[devonpallison]

I could use a little more information here. After reading this, I'm still not sure why anyone would use the dryRun method. I can validate my SQL context when I run evaluate(). What's the advantage of doing it with dryRun()? What does "Inspecting the query plan" mean? I'm not sure how this would help build tools that work with SQL queries either

[devonpallison]

I see further down you list "Fast validation without execution"- this seems like a good point to add here