jsonb_extract_path_text() and json_extract_path_text()

Purpose: Provide the identical functionality to the #>> operator.

Signature For the jsonb variant:

input value:       jsonb, VARIADIC text
return value:      text

Notes: The result of jsonb_extract_path_text() bears the same relationship to the result of its jsonb_extract_path() counterpart as does the result of the #>> operator to that of its #> counterpart. For the same reason that there is no reason to prefer jsonb_extract_path() over #>, there is no reason to prefer jsonb_extract_path_text() over #>>.