Make parsing error easier to understand

[martynydbt]

Housekeeping

• I am a maintainer of dbt-core

Short description

Context:

Someone set severity to warning which is not a valid severity (only warn and error are valid):

From Gerda: This comes from jsonschema validation which often leads to somewhat strange and cryptic errors

Origin:

Coming from here

Acceptance criteria

The error is easy to understand.
"Severity can only be set to Warn or Error"

Suggested Tests

validate that the parsing error raises as expected

Impact to Other Teams

IDE surfaced, impact label is added.

Will backports be required?

No

Context

No response

[FishtownBuildBot]

Opened a new issue in dbt-labs/docs.getdbt.com: dbt-labs/docs.getdbt.com#5330

[runleonarun]

@martynydbt I closed the docs issue because this is already documented here: https://docs.getdbt.com/reference/resource-configs/severity