"Drain Before Delete" support for RKE2 machine pools

[snasovich]

Detailed Description
For RKE1-provisioned clusters, there is currently an option to specify whether nodes should be drained before deletion for each node pool:

For RKE2-provisioned clusters, we want the same functionality to be available, probably by adding a checkbox somewhere on the base pool details section highlighted below:

Context
This is needed for RKE2 provisioning parity with RKE1

Additional Details
Backend support is needed: rancher/rancher#35274

[snasovich]

Backend changes done per rancher/rancher#35274, should no longer be blocked by backend. If clarifications are needed, please contact @jakefhyde who implemented backend changes (there is a good summary here).

[ronhorton]

PASS verified in 2.6-head Commit ID cd3c9d7

1. created downstream rke2 cluster
2. 'drain before delete' is available now for rke2
3. brought up cluster
4. checked logs - no errors
5. deleted cluster
6. cluster was deleted & removed from downstream provider

[sowmyav27]

Reopening to test a few more scenarios

[anupama2501]

Verified on v2.6-head 8c785a1 as part of this issue:
rancher/rancher#35274 (comment)

[jtravee]

Confirmed with @catherineluse and @gaktive to add release note label.