Add webui::FlagsIdentifier annotation key tip

[diegoperezurruti]

For the FlagsIdentifier, you dont necessary need to use an indexed string parameter, you can also assign a non-indexed sp_ReadOnlyFlag_d if you want to make it readonly for all combinations; and if you do want to use indexes, add definition for only the tupple you need, in this case, with the $ 'identifier_name' as domain.

[diegoperezurruti]

Using indexed string parameters can be huge in therms of memory use and crash the page and the whole computer as we have experienced recently with Peapod TNT App

[diegoperezurruti]

Adding this to the documentation explicitly or as a key tip could be very useful to prevent future dev issues