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/config/mod.rs

@@ -134,6 +134,15 @@ pub struct Config {
     #[serde(default = "default_ip_range_denylist")]
     pub ip_range_denylist: Vec<String>,
 
+    #[serde(default = "Vec::new")]
+    pub url_preview_domain_contains_allowlist: Vec<String>,
+
+    #[serde(default = "Vec::new")]
+    pub url_preview_domain_explicit_allowlist: Vec<String>,
+
+    #[serde(default = "Vec::new")]
+    pub url_preview_url_contains_allowlist: Vec<String>,
+
     #[serde(default = "RegexSet::empty")]
     #[serde(with = "serde_regex")]
     pub forbidden_room_names: RegexSet,
@@ -349,6 +358,18 @@ impl fmt::Display for Config {
             ("Forbidden room names", {
                 &self.forbidden_room_names.patterns().iter().join(", ")
             }),
+            (
+                "URL preview domain contains allowlist",
+                &self.url_preview_domain_contains_allowlist.join(", "),
+            ),
+            (
+                "URL preview domain explicit allowlist",
+                &self.url_preview_domain_explicit_allowlist.join(", "),
+            ),
+            (
+                "URL preview URL contains allowlist",
+                &self.url_preview_url_contains_allowlist.join(", "),
+            ),
         ];
 
         let mut msg: String = "Active config values:\n\n".to_owned();