Add method to _connection_keys

[jtcohen6]

resolves #335

Description

• Add {{ target.method }} to Jinja context
• This allows us to have clearer logs + easier debugging when running into errors like The SQL contains 0 parameter markers, but x parameters were supplied (e.g. [CT-502] [Bug] dbt seed returning '0 parameter markers' error  #334)

Checklist

• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt-spark next" section.

[jtcohen6]

This didn't "just work" in the way I might have hoped :) will take a bit more experimentation. The right answer here may just look like additional logging within connection.py—the same SQL, after sqlparam conversion—if the swap from ? for %s can't happen within the templating/Jinja layer.