Fix sign out not working when a cluster is selected

[mendaomn]

Description

This PR fixes an issue, making the logout button linking to non-existing pages, instead of properly logging out the user.

Changes

• make the signout link to be relative to the domain instead of relative to the current path
• add i18n strings

How Has This Been Tested?

• manually

References

• Cloudscape documentation

PR Quality Checklist

• [ ] I added tests to new or existing code
• [x] I removed hardcoded strings and used our i18n solution instead (see here)
• [ ] 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)
• [x] I checked that login and logout work as expected

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