[metrics] Fix io metrics documentation references (#10630)
[metrics] Fix io metrics documentation references (#10630)

* Fix broken image & dashboard links in rendered online documentation
* Fix prerequisite version in documentation (do not use milestone version)

Signed-off-by: Robert Bach <c6a4fe0b25a74497e966f279f5186c99e5ce30e3@mortalsilence.net>
paulianttila/openhab2,paulianttila/openhab2,paulianttila/openhab2