scripted-diff: Rename PACKAGE_* variables to CLIENT_*

This change ensures consistent use of the `CLIENT_` namespace everywhere
in the repository.

-BEGIN VERIFY SCRIPT-

ren() { sed -i "s/\<$1\>/$2/g" $( git grep -l "$1" ./cmake ./src :\(exclude\)./src/secp256k1 ./test ) ; }

ren PACKAGE_NAME      CLIENT_NAME
ren PACKAGE_VERSION   CLIENT_VERSION_STRING
ren PACKAGE_URL       CLIENT_URL
ren PACKAGE_BUGREPORT CLIENT_BUGREPORT

-END VERIFY SCRIPT-

test/functional/wallet_multiwallet.py

@@ -204,7 +204,7 @@ class MultiWalletTest(BitcoinTestFramework):
         self.restart_node(0, ['-nowallet', '-walletdir=' + competing_wallet_dir])
         self.nodes[0].createwallet(self.default_wallet_name)
         if self.options.descriptors:
-            exp_stderr = f"Error: SQLiteDatabase: Unable to obtain an exclusive lock on the database, is it being used by another instance of {self.config['environment']['PACKAGE_NAME']}?"
+            exp_stderr = f"Error: SQLiteDatabase: Unable to obtain an exclusive lock on the database, is it being used by another instance of {self.config['environment']['CLIENT_NAME']}?"
         else:
             exp_stderr = r"Error: Error initializing wallet database environment \"\S+competing_walletdir\S*\"!"
         self.nodes[1].assert_start_raises_init_error(['-walletdir=' + competing_wallet_dir], exp_stderr, match=ErrorMatch.PARTIAL_REGEX)