Clear selected cluster when the region is changed

[mtfranchetto]

Description

Fixes a bug where an error message was flashed after switching the region.

How Has This Been Tested?

• Selected a cluster, changed the region and verified to error message appears

PR Quality Checklist

• [x] I added tests to new or existing code
• [ ] I removed hardcoded strings and used our i18n solution instead (see here)
• [x] I made sure no sensitive info gets logged at any time in the codebase (see here) (e.g. no user info or details, no stacktraces, etc.)
• [ ] I checked that infrastructure/update_infrastructure.sh runs without any error
• [x] I checked that npm run build builds without any error
• [x] I checked that clusters are listed correctly
• [ ] I checked that a new cluster can be created (config is produced and dry run passes)
• [ ] I checked that login and logout work as expected

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