node driver: remove maxVolumesPerNode constant

[sauterp]

Description

Ensuring that the maximum number of volumes per node is not overstepped is the API's responsability, hence we remove the limitation in the CSI.

Checklist

(For exoscale contributors)

• [x] Changelog updated (under Unreleased block)
• [x] Integration tests OK

[sauterp]

[sc-91235]

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #91235: CSI: respect max number of volumes per node.