Improve the debug help command message (#9098)

cleanups:
1: Re-introduce debug leak subcommand in help text.
Mistankenly deleted in https://github.com/redis/redis/pull/5531

2: Formatted the text.
Some text lacks commas resulting in no line breaks.

3: Supplementary debug restart command descriptions of delay arg.

src/debug.c

@@ -389,14 +389,14 @@ void debugCommand(client *c) {
 "    Server will sleep before flushing the AOF, this is used for testing.",
 "ASSERT",
 "    Crash by assertion failed.",
-"CHANGE-REPL-ID"
+"CHANGE-REPL-ID",
 "    Change the replication IDs of the instance.",
 "    Dangerous: should be used only for testing the replication subsystem.",
 "CONFIG-REWRITE-FORCE-ALL",
 "    Like CONFIG REWRITE but writes all configuration options, including",
 "    keywords not listed in original configuration file or default values.",
-"CRASH-AND-RECOVER <milliseconds>",
-"    Hard crash and restart after a <milliseconds> delay.",
+"CRASH-AND-RECOVER [<milliseconds>]",
+"    Hard crash and restart after a <milliseconds> delay (default 0).",
 "DIGEST",
 "    Output a hex signature representing the current DB content.",
 "DIGEST-VALUE <key> [<key> ...]",
@@ -404,6 +404,8 @@ void debugCommand(client *c) {
 "ERROR <string>",
 "    Return a Redis protocol error with <string> as message. Useful for clients",
 "    unit tests to simulate Redis errors.",
+"LEAK <string>",
+"    Create a memory leak of the input string.",
 "LOG <message>",
 "    Write <message> to the server log.",
 "HTSTATS <dbid>",
@@ -430,7 +432,7 @@ void debugCommand(client *c) {
 "POPULATE <count> [<prefix>] [<size>]",
 "    Create <count> string keys named key:<num>. If <prefix> is specified then",
 "    it is used instead of the 'key' prefix.",
-"DEBUG PROTOCOL <type>",
+"PROTOCOL <type>",
 "    Reply with a test value of the specified type. <type> can be: string,",
 "    integer, double, bignum, null, array, set, map, attrib, push, verbatim,",
 "    true, false.",
@@ -438,7 +440,7 @@ void debugCommand(client *c) {
 "    Save the RDB on disk and reload it back to memory. Valid <option> values:",
 "    * MERGE: conflicting keys will be loaded from RDB.",
 "    * NOFLUSH: the existing database will not be removed before load, but",
-"      conflicting keys will generate an exception and kill the server."
+"      conflicting keys will generate an exception and kill the server.",
 "    * NOSAVE: the database will be loaded from an existing RDB file.",
 "    Examples:",
 "    * DEBUG RELOAD: verify that the server is able to persist, flush and reload",
@@ -447,8 +449,8 @@ void debugCommand(client *c) {
 "      existing RDB file.",
 "    * DEBUG RELOAD NOSAVE NOFLUSH MERGE: add the contents of an existing RDB",
 "      file to the database.",
-"RESTART",
-"    Graceful restart: save config, db, restart.",
+"RESTART [<milliseconds>]",
+"    Graceful restart: save config, db, restart after a <milliseconds> delay (default 0).",
 "SDSLEN <key>",
 "    Show low level SDS string info representing `key` and value.",
 "SEGFAULT",