Remove dedicated cost monitoring page

[mendaomn]

Description

This PR removes the dedicated cost monitoring page. It is related to #218 , but can be safely merged in any order since the whole feature is behind an experimental flag

PR Quality Checklist

• [ ] I added tests to new or existing code
• [ ] I removed hardcoded strings and used react-i18next library (useTranslation hook and/or Trans component), see an example 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 made sure that any GitHub issue solved by this PR is correctly linked
• [ ] I checked that infrastructure/update_infrastructure.sh runs without any error
• [x] I checked that npm run build builds without any error
• [ ] 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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