Fix pg_amcheck --skip option parameter handling

The skip options set for all-visible and all-frozen were incorrect
as they used space rather than hyphen, causing a syntax error when
invoked. Also, the option for not skipping any pages at all, none,
was documented but not implemented.

Backpatch through 14 where pg_amcheck was introduced.

Bug: #17149
Reported-by: Chen Jiaoqian <chenjq.jy@fujitsu.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/17149-5918ea748da36b15@postgresql.org
Backpatch-through: 14

src/bin/pg_amcheck/pg_amcheck.c

@@ -397,9 +397,11 @@ main(int argc, char *argv[])
 				break;
 			case 6:
 				if (pg_strcasecmp(optarg, "all-visible") == 0)
-					opts.skip = "all visible";
+					opts.skip = "all-visible";
 				else if (pg_strcasecmp(optarg, "all-frozen") == 0)
-					opts.skip = "all frozen";
+					opts.skip = "all-frozen";
+				else if (pg_strcasecmp(optarg, "none") == 0)
+					opts.skip = "none";
 				else
 				{
 					pg_log_error("invalid argument for option %s", "--skip");