Remove all IMAP-Folder-Handling options for chatmail accounts

[hpk42]

Chatmail addresses do not need any special imap-folder settings and it makes sense, also for the server-side chatmail setup, to not have any folders because we don't need it, and fresh instant-onboarding users don't need to think about it even in advanced settings. Not sure how to best signal to UIs to not expose these options, maybe similar to #5380 with a "NOFOLDERS" capability.

[Simon-Laux]

maybe just a readonly config key that the ui can read

[iequidoo]

Maybe add a function Context::is_configurable() that should be checked for options that are not always configurable?

[r10s]

Maybe add a function Context::is_configurable() that should be checked for options that are not always configurable?

i think, this is a bit over the top, eg. having 4 states that could in theory be all on/off in all combinations. UI would need to think over how to hide a group and whatnot then.

i would go for a single switch, and yes, reusing get_config() for that seems to be a pragmatic, simple approach not requiring new API - also, we have already read-only options there, so that would not even be sth. new

[r10s]

IMAP-Folder options are removed in UIs:

• for android in hide IMAP folder options on chatmail deltachat-android#3050
• for ios in for chatmail accounts, hide some not useful settings deltachat-ios#2166
• for desktop in hide irrelevant advanced settings for chatmail users deltachat-desktop#3823