doveadm lists nonexistent HTTP commands

[sirainen]

Some commands are available only in CLI, not via HTTP:

• config
• dump
• exec
• help
• pw
• compress connect
• auth lookup
• auth login
• auth test

Add some flag so these are listed only as available with CLI, and clearly marked not available via HTTP.

[slusarz]

"config" and "help" didn't exist, so those were added in #1386