kubeconfig-default-ttl-minutes setting should be made to accept only integer values

[anupama2501]

Setup

Rancher version: 2.6-head 78017e6
Browser type & version: Chrome

Describe the bug
Currently we can set the value for kubeconfig-default-ttl-minutes setting in the UI to any non-integer values. By accidentally setting the value to a non-integer value, when we try to download the kubeconfig button, the file will not be downloaded and fails with an error

To Reproduce

1. On rancher v2.6-head, navigate to global settings >> Settings >> set kubeconfig-token-ttl-minutes to 2/
2. Navigate to local explorer, click on download kubeconfig button

Result
Download fails with the error
message: "failed to get default token TTL: failed to parse setting 'kubeconfig-default-ttl-minutes': error parsing token ttl: time: unknown unit \";m\" in duration \"2;m\""
Expected Result
UI not allowing to save non integer values.

Related: #6120

[anupama2501]

Verified on v2.6-head 6629e3e

Input takes only integer values.