feat: URL preview support

from upstream MR https://gitlab.com/famedly/conduit/-/merge_requests/347
with the following changes (so far):
- remove hardcoded list of allowed hosts (strongly disagree with this,
even if it is desired, it should not be harcoded)
- add more allow config options for granularity via URL contains,
host contains, and domain is (explicit match) for security
- warn if a user is allowing all URLs to be previewed for security reasons
- replace an expect with proper error handling
- bump webpage to 2.0
- improved code style a tad

Co-authored-by: rooot <hey@rooot.gay>
Signed-off-by: rooot <hey@rooot.gay>
Signed-off-by: strawberry <strawberry@puppygock.gay>

src/service/globals/mod.rs

@@ -390,6 +390,18 @@ impl Service<'_> {
         &self.config.emergency_password
     }
 
+    pub fn url_preview_domain_contains_allowlist(&self) -> &Vec<String> {
+        &self.config.url_preview_domain_contains_allowlist
+    }
+
+    pub fn url_preview_domain_explicit_allowlist(&self) -> &Vec<String> {
+        &self.config.url_preview_domain_explicit_allowlist
+    }
+
+    pub fn url_preview_url_contains_allowlist(&self) -> &Vec<String> {
+        &self.config.url_preview_url_contains_allowlist
+    }
+
     pub fn forbidden_room_names(&self) -> &RegexSet {
         &self.config.forbidden_room_names
     }