updated SA_Proof functions to use domain separator hash key

src/cryptonote_config.h

@@ -359,6 +359,7 @@ namespace config
   const constexpr char HASH_KEY_MULTISIG_TX_PRIVKEYS_SEED[] = "multisig_tx_privkeys_seed";
   const constexpr char HASH_KEY_MULTISIG_TX_PRIVKEYS[] = "multisig_tx_privkeys";
   const constexpr char HASH_KEY_TXHASH_AND_MIXRING[] = "txhash_and_mixring";
+  const constexpr char HASH_KEY_SA_PROOF[] = "SPARC_sa_proof_domain_separator";
 
   // Multisig
   const uint32_t MULTISIG_MAX_SIGNERS{16};