Retrieve CSRF token before each mutation

[mtfranchetto]

Description

Align the frontend after the backend changes for the new CSRF token generation mechanism #495

Changes

• add the ability to pass headers to the executeRequest function
• moved the CSRF token retrieval from the initial state to the executeRequest function
• stub executeRequest instead of axios in CreateCluster tests, otherwise the CSRF check complains

How Has This Been Tested?

Run the portal locally and verified:

• no CSRF call is made at the startup
• a CSRF token is retrieved before each mutation

PR Quality Checklist

• [x] I added tests to new or existing code
• [ ] 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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