leverage 2-step upgrade mechanism to upgrade longhorn to 1.11 in sylva 1.7

Since longhorn only supports upgrades from version N to version N+1, we were limited to one version bump of longhorn per Sylva version up to now.

Version mapping:

sylva	longhorn
1.5	1.8
1.6	1.9
1.7	1.10

As a consequence Sylva is lagging behind in term of longhorn versions: longhorn 1.11 has been released in January 26, but it has not been integrated in Sylva up to now (May) as we were limited to a single major version bump.

Thanks to the recent introduction of the multi-step upgrade mechanism in (see #3782 (closed)), we'll be able to upgrade to upgrade longhorn to 1.11 in Sylva 1.7 by performing two consecutive upgrades.

For that purpose we'll need to use a similar mechanism to what has been proposed in !7493 (merged) and !7614 (merged) to compute the longhorn version and optionally request an additional reconciliation.