[UDFs] add function `type` property

[graciegoheen]

Housekeeping

• I am a maintainer of dbt-core

Short description

add a type property to function - “is this function a UDF (scalar), UDAF (aggregate), UDTF (table)?”

Acceptance criteria

• new type function property

functions:
	- name: string # Required
	  description: string # Optional
	  type: scalar # Optional, defaults to scalar. Will eventually also support aggregate and table 

• p0 support default scalar
• p1 support additional aggregate type (UDAF)
• p2 support additional table type (UDTF)

Context

No response

[FishtownBuildBot]

Opened a new issue in dbt-labs/docs.getdbt.com: dbt-labs/docs.getdbt.com#7957