Change multi cluster docs link to new location

[david-martin]

The new url is https://docs.kuadrant.io/getting-started-multi-cluster-ocm, which will be live after Kuadrant/docs.kuadrant.io#97 lands.
It's just the url that is changing. The page and content is the same as before.
This is to accommodate a move of all mgc & ocm related content into a separate sub-section in the docs.
The previous url https://docs.kuadrant.io/getting-started-multi-cluster will still be live, but point to a new page that doesn't use ocm or mgc.

[jasonmadigan]

👀

[jasonmadigan]

/lgtm
/approve

[openshift-ci]

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