docs: rework connection parameter reference in Thrift-vs-Kernel table format

Drop the SEA column (backend is being deprecated) and restructure the doc to
match the databricks-sql-nodejs connection-parameter reference (#457): a
two-backend Thrift/Kernel table per section with a ✅/❌/⚠️/— legend, a
'Sources of truth' list, and a 'Summary of gaps'.

Co-authored-by: Isaac
Signed-off-by: eric-wang-1990 <e.wang@databricks.com>

Author: eric-wang-1990

README.md

@@ -23,7 +23,7 @@ For the latest documentation, see
 - [Azure Databricks](https://docs.microsoft.com/en-us/azure/databricks/dev-tools/python-sql-connector)
 
 For a full reference of every `sql.connect(...)` keyword argument — type,
-default, per-backend support (Thrift / SEA / Kernel), and meaning — see
+default, per-backend support (Thrift vs Kernel), and meaning — see
 [`docs/connection-parameters.md`](docs/connection-parameters.md).
 
 ## Quickstart