Add Edit Preference functionality

Allow Editing both Global preferences and Channel Preferences, according to mocks: https://codimd.web.cern.ch/s/BkiF_r8Nw#Option-1

In the Channel Preferences page, section "Global Preferences" prefs should still not be editable, just enable/disable as is.

Should open a modal equal to create preference, pre filled that just edits.

Check if BE already as an API for editing a preference.