Enhance multipathing documentation for XCP-ng

[manfuin]

Hi! This PR is aimed to add information about multipath management in XCP-ng to clarify the expectations when verifying visible paths on host.

I spend quite a time to understand why the multipath device is not created on the host despite the default config has find_multipaths set to yes. I hope this small extra info notice in the documentation can save time for other people like me.

I used to the practice that I have to check that multipath is operational before I am going to do something with multipath device from generic Linux experience.

This assumption is clearly wrong in Storage Manager case, and Storage Manager source code is clearly shows it is managing wwids and basically all aspects of multipath management on its own and not relying on paths auto-assembly by multipathd. I trully believe this is important to know at the start.

Kind regards,
Andrii

Before submitting the pull request, you must agree with the following statements by checking both boxes with a 'x'.

• "I accept that my contribution is placed under the CC BY-SA 2.0 license [1]."
• "My contribution complies with the Developer Certificate of Origin [2]."

[1] https://creativecommons.org/licenses/by-sa/2.0/
[2] https://docs.xcp-ng.org/project/contributing/#developer-certificate-of-origin-dco

[stormi]

It looks good to me, but I added @ylebris as reviewer for another pair of eyes.