Update CREATE TRIGGER syntax to use EXECUTE FUNCTION

What does this MR do?

Change occurrences of CREATE TRIGGER ... EXECUTE PROCEDURE to CREATE TRIGGER ... EXECUTE FUNCTION. The PROCEDURE keyword was the previous required syntax on PG9.6, but as of PG11 is deprecated. In PG12, internal PG metadata use the FUNCTION keyword, so we should use that as well to be consistent.

See the linked issue for details: #227089 (closed)

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