Use a documentation-only IP to avoid confusion and follow best practice.
This prevents irritation when users or scanners see a private address in
samples and wonder if rsyslog is trying to contact it.
Impact: Visible change in sample payloads, tests, and docs (host field).
Technical: Replace the hardcoded "172.20.245.8" in imdiag's generated
messages with a constant default hostname "192.0.2.8" from RFC 5737
(TEST-NET-1). Update tests (e.g., omrabbitmq, perctile, mmexternal,
clickhouse) and template examples to match. No API/ABI change; no effect
on action queues, OMODTX, retry/duplicate semantics, or HUP behavior.
This is purely about sample message contents emitted by the diag tool.
Before/After: samples used 172.20.245.8 -> now 192.0.2.8.
See also: https://gitee.com/src-openeuler/rsyslog/issues/I7V4I8
Fixes: https://github.com/rsyslog/rsyslog/issues/6190
commit 8791323c92039 fixed invalid handling of first space in MSG.
This broke some test, but was not detected at the time of its merge.
This is now fixed with this follow-up commit.
