RKE2 snapshot S3 configuration support

[snasovich]

Detailed Description
Currently, S3 configuration cannot be set on UI for RKE2 snapshots - I believe it was disabled at some point during 2.6.0 release due to issues (rancher/rancher#34417 is about on-demand S3 snapshots, but probably affects scheduled ones too.)
The UI existed before per rancher/rancher#34088 (comment), so it will need to be re-enabled once backend issues are fixed. This issue is to track this effort.

Context
Needed for RKE2 provisioning parity with RKE1

[gaktive]

UI should be pretty much in place once the backend work is done.

[gaktive]

Backend item is now in QA so this looks ready to work on. @snasovich, is this good for UI to work on?

[gaktive]

Hopefully the overlap with #4539 means that this is simple.

[snasovich]

@gaktive , this should be unblocked now, however we need @Oats87 to provide a summary of his changes and impact on UI for this. There may be no impact on this specific issue, but there is certainly input needed for #4539. As well as I believe there is a change needed for how UI shows snapshots which will need to be a separate UI issue (sorry!).

@Oats87 , could you please provide the "impact to QA / UI" on rancher/rancher#34417 (unless it's provided elsewhere - please point us to it).

[snasovich]

Note there are no changes in how snapshot (and S3 configuration) is passed as a result of changes done per rancher/rancher#34417.

[timhaneunsoo]

Test Environment:

Rancher version: v2.6-head 3df76e4
Rancher cluster type: HA
Docker version: 20.10

Downstream cluster type: RKE2 EC2

---

Testing:

Tested this issue with the following:

1. Create RKE2 Cluster
2. Under etcd configuration, enable backup Snapshots to S3
3. Fill out fields to set up S3 bucket
4. Confirm edits are made in the yaml

Result - Pass

The UI configuration is available.

Edits made in the UI are also reflected in the yaml