...ervenors in agency proceedings under the APA. The provision of the APA governing hearings provides *257 that only parties to the hearings are entitled "to respond and present evidence on all issues involved." OCGA §
50-13-13 (a) (3). Moreover, OCGA §
46-2-58, enacted along with OCGA §
46-2-59, sets out procedures for conducting PSC hearings, and provides, similarly to OCGA §
50-13-13 (a) (3), that "[t]he hearing officer or commission shall permit only the Commissioners, the hearing officer, the parties, or the attorneys of record of the Commissioners, hearing officers, or parties to examine or cross-examine witnesses, except with the consent of the witness." OCGA §
46-2-58 (c)....