recognize t.me proxy qr codes (#5895)

this PR adds the type DC_QR_SOCKS5_PROXY to `dc_check_qr()` for
**supporting telegram proxy QR codes**. if returned, the UI should ask
the user if they want to us the proxy and call
`dc_set_config_from_qr();` afterwards (plus maybe `dc_configure()`).

idea is to improve our proxy story, follow ups may be:

- in UI, - move proxy out of "Account & Password", as a **separate
"Proxy Activity"** (it should stay in "Advanced" for now, however, below
"Server", which might be moved up)

- allow **opening the "Proxy Activity" from the welcome screens**
three-dot-menu (that would also solve a long standing issue that
entering the email address bypasses the proxy

- show proxy usage in the "Connectivity View" and/or add an **icon** to
the main chatlist screen (beside three-dot menu) in case some proxy is
in use; tapping this icon will open the "Proxy Activity"

- the the new "Proxy Activity", add a **share / show proxy QR code**
button. that would generate invite links in the form
`https://i.delta.chat/socks#...` - so that tapping then opens the app.
support for these links need to be added to core then.

- handle a list of proxies in core, offer selection in UI. the list
could be one for all profiles and could be filled eg. by normal invite
links or other channels

---------

Co-authored-by: iequidoo <117991069+iequidoo@users.noreply.github.com>

deltachat-jsonrpc/src/api/types/qr.rs

@@ -44,6 +44,12 @@ pub enum QrObject {
         domain: String,
         instance_pattern: String,
     },
+    Socks5Proxy {
+        host: String,
+        port: u16,
+        user: Option<String>,
+        pass: Option<String>,
+    },
     Addr {
         contact_id: u32,
         draft: Option<String>,
@@ -152,6 +158,17 @@ impl From<Qr> for QrObject {
                 domain,
                 instance_pattern,
             },
+            Qr::Socks5Proxy {
+                host,
+                port,
+                user,
+                pass,
+            } => QrObject::Socks5Proxy {
+                host,
+                port,
+                user,
+                pass,
+            },
             Qr::Addr { contact_id, draft } => {
                 let contact_id = contact_id.to_u32();
                 QrObject::Addr { contact_id, draft }