Settings page improvements

[penk85]

WPC-1081: Improvements on settings page:

• ✔️ disable save button if nothing is changed
• ✔️ introduce cancel button to undo the unsaved changes
• ✔️ throw warning when clicking on save: i.e. “are you sure you want to change these settings?” with the details of what settings will be updated
• ✔️ Added missing setting for invoice reminder max tries
• throw warning when try to leave page with unsaved changes: this is partially implemented with the warning showing when user refreshes the page, closes the tab or other window events but does not get triggered from React route changes. This should be handled in a separate ticket.

[github-actions]

PR 880 with branch wpc-1081-settings-unsaved-changes-dialog has been deployed to:

• Website: https://wpc1081set.wepublish.dev
• Editor: https://editor.wpc1081set.wepublish.dev
• Public API: https://api.wpc1081set.wepublish.dev
• Privat API: https://api.wpc1081set.wepublish.dev/admin
• Media: https://media.wpc1081set.wepublish.dev