Should not be able to add the same key for taints

Created by: wenxin-01

Versions Used KubeSphere: dev:latest

Preset conditions There is cluster 'default' have node and edge node 'edgenode-wdkk'

How To Reproduce Steps to reproduce the behavior:

1. Go to cluster 'default'
2. Click on 'Nodes'
3. Click on 'Edge nodes'
4. Go to edge node 'edgenode-wdkk'
5. Clcik on 'more' --> clcik on 'Taint Management'
6. Add repeated key 'node-role.kubernetes.io/edge'
7. click on 'Save'

Expected behavior The page has an error message and cannot be saved

Actual behavior Saved successfully

/kind bug /assign @leoendless /milestone 3.1.0 /priority medium