Create missing helper functions to get values out of JSON object arrays.

This already exists:

For each element of the jsonb_array take the value of field; concatenate them using space as separator

These functions are missing:

Take each value of the field attribute of the jsonb_array elements where the filterkey of the element has filtervalue; concate the values using space as separator.

Return the value of the field attribute of the first jsonb_array element where filterkey has filtervalue.

This requirement has been asked for on slack several times. One use case is the identifiers array where one may want to select the first oclc number for matching.