MINOR: cli: correct commentary and replace 'set global-key' name

Correct a commentary in in include/haproxy/global-t.h and include/haproxy/tools.h
Replace the CLI command 'set global-key <key>' by 'set anon global-key <key>' in
order to find it easily when you don't remember it, the recommandation can guide
you when you just tap 'set anon'.

No backport needed, except if anonymization mechanism is backported.
4 files changed