Update docs on structured logging for v1.4 changes

[jtcohen6]

Contributions

• I have read the contribution docs, and understand what's expected of me.

Link to the page on docs.getdbt.com requiring updates

https://docs.getdbt.com/reference/events-logging
https://docs.getdbt.com/reference/dbt-jinja-functions/env_var#custom-metadata

What part(s) of the page would you like to see updated?

Lots of changes to structured logging coming in v1.4. Fuller description TK.

Most relevant:

• Description of proto class definitions, what this means at a high level, with redirect to technical details in https://github.com/dbt-labs/dbt-core/blob/main/core/dbt/events/README.md
• [If we get to it in time] Reorg of basic event structure into two top-level keys ([CT-1549] Reorganize structure of logging events to have two top level keys dbt-core#6311)
• node_info will include the meta dictionary, with custom user-supplied values: Include the meta field in the node_info property description #2632
• Metadata env vars will appear on all log events: Allow custom metadata to be attached to every log dbt-core#5999

Additional information

No response