feat: increase service URL size limit (#608)

Fixes /~https://github.com/KILTprotocol/ticket/issues/3131.

The ticket mentions that 500 would be a good new limit for the inbound
request we had. Reading elsewhere online, such as
[here](https://stackoverflow.com/a/417184) it seems that 2000 characters
is a good upper bound limit for URLs. Since every change would require a
runtime upgrade, I would rather make the value future proof and set it
to 2000 directly.

runtimes/common/src/constants.rs

@@ -385,7 +385,7 @@ pub mod did {
 	pub const MAX_SERVICE_ID_LENGTH: u32 = 50;
 	pub const MAX_SERVICE_TYPE_LENGTH: u32 = 50;
 	pub const MAX_NUMBER_OF_TYPES_PER_SERVICE: u32 = 1;
-	pub const MAX_SERVICE_URL_LENGTH: u32 = 200;
+	pub const MAX_SERVICE_URL_LENGTH: u32 = 2_000;
 	pub const MAX_NUMBER_OF_URLS_PER_SERVICE: u32 = 2;
 
 	parameter_types! {