[Feature]: Add sql-datatype to the SDK discovery and catalog.

[BuzzCutNorman]

Feature scope

Taps (catalog, state, stream maps, etc.)

Description

It would be very helpful if SDK based taps during the discovery process of a database grabbed column data types and placed them into the catalog metadata area for the column in the field of sql-datatype. The sql-datatype field is a reserved keyword mentioned in the singer discovery documentation.

https://github.com/singer-io/getting-started/blob/master/docs/DISCOVERY_MODE.md#metadata

Keyword	Tap Type	Discoverable?	Description
sql-datatype	database	discoverable	Represents the datatype of the database column

        {
          "breadcrumb": [
            "properties",
            "name"
          ],
          "metadata": {
            "sql-datatype": "varchar(255)",
            "selected-by-default": true
          }
        }

[stale]

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[edgarrmondragon]

Related: #1903