feat: client version information (#8557)

> we aim to inform about updates for installations outside of any
appstore soon.
>
> there is already a PR on android at
https://github.com/deltachat/deltachat-android/pull/4582, however, the
information about "update available" is a mockup there.
>
> in general, there are 3 ideas around about how to gather the "update
available" infomation - (1) checking a central url, (2) let contacts
provide information, (3) let relay provide information. on various
one-to-one discussions, outcome is that (3) is the most reasonable way
to go.

this PR is about reading update information via IMAP metadata from the
relay.

it is up to the UI to call `get_app_version()` at a reasonable time and
frequency, see comment in the code. when called, `get_app_version()`
iterates over all known profiles and relays and checks for version
information, returning the newest for the given scope.

we do not use an event, as that is tricky wrt changes - we do not know
if other relays report later a newer version. we also do not cache
anything, to prevent bad relays avoiding us to update permanently. also
it is easier :)

<details>
<summary>outdated notes and questions</summary>

- ~~it is up to the clients to get the needed information, we could let
core filter, but it seems easy enough the other way round, and may have
debug advantages, one can iterate etc.~~ EDIT: we now filter in core,
this also makes the jsonrpc part easier, see review comments

- when is IMAP METADATA actually read? when are they ready? is that
really the correct place? i am up to change that, but beware, this is
not really my expertise, so someone else may need to take over :)
EDIT: see below, IMAP METADATA is read on connection, before fetching
starts, usually fast enough

- relay part is missing. once the format is settled and discussed
shortly here, that should be done soon as well. but this is definitely
not my expertise and needed to be done by someone else :)

- key for IMAP METADATA is `/shared/vendor/deltachat/appversions` -
shall we continue use `deltachat` for compatibility or so? `chatmail`
seems to be more correct
EDIT: we stay with the current
</details>

relay counterpart issue: https://github.com/chatmail/relay/issues/1037

cc @link2xt @Hocuri @hpk42

---------

Co-authored-by: holger krekel <holger@merlinux.eu>

deltachat-jsonrpc/src/api.rs

@@ -64,6 +64,7 @@ use self::types::{
         JsonrpcMessageListItem, MessageNotificationInfo, MessageSearchResult, MessageViewtype,
     },
 };
+use crate::api::types::appversions::JsonrpcAppSource;
 use crate::api::types::chat_list::{ChatListItemFetchResult, get_chat_list_item_by_id};
 use crate::api::types::login_param::TransportListEntry;
 use crate::api::types::qr::{QrObject, SecurejoinSource, SecurejoinUiPath};
@@ -2788,6 +2789,39 @@ impl CommandApi {
             Err(anyhow!("chat with id {chat_id} doesn't have draft message"))
         }
     }
+
+    /// Get version information of a specific client and source
+    /// across all configured accounts and transports.
+    ///
+    /// Returns the source with the highest `version_integer`.
+    /// If no matching version information is available at all, `None` is returned.
+    ///
+    /// UIs shall call the function after a reasonable time after app start,
+    /// when most relays have reported the information they have, say 30 seconds.
+    /// After that, once a day.
+    /// (it is accepted if by the simple approach an update message is delayed.
+    /// an event was considered, but that seemed more complex for few benefit:
+    /// as we do not know if "late" relays will report "better" versions,
+    /// also there we would work with timeouts etc.)
+    ///
+    /// If the reported `version_integer` is larger than the running app version,
+    /// the UI shall report to the user, that an update is available,
+    /// and, if possible, offer a direct update by the given URL.
+    ///
+    /// Security note: consumers need to verify themselves
+    /// that downloaded app files are valid before installing them.
+    async fn get_app_version(
+        &self,
+        client_id: String,
+        source_id: String,
+    ) -> Result<Option<JsonrpcAppSource>> {
+        let accounts = self.accounts.read().await;
+        Ok(
+            deltachat::appversions::get_app_version(&accounts, &client_id, &source_id)
+                .await?
+                .map(JsonrpcAppSource::from_core_type),
+        )
+    }
 }
 
 // Helper functions (to prevent code duplication)