Remove unneeded 'static lifetimes on &strs in constants (#8698)

This PR removes unneeded `'static` lifetimes on `&str`s stored in
`const` declarations.

This addresses some Clippy lints about
[`redundant_static_lifetimes`](https://rust-lang.github.io/rust-clippy/master/index.html#/redundant_static_lifetimes).

In item-level `const` declarations we can rely on lifetime elision and
use the default `'static` lifetime.

Note that associated constants still require an explicit `'static`
lifetime, as explained in
https://github.com/rust-lang/rust/issues/115010.

Release Notes:

- N/A

crates/rpc/src/notification.rs

@@ -3,8 +3,8 @@ use serde::{Deserialize, Serialize};
 use serde_json::{map, Value};
 use strum::{EnumVariantNames, VariantNames as _};
 
-const KIND: &'static str = "kind";
-const ENTITY_ID: &'static str = "entity_id";
+const KIND: &str = "kind";
+const ENTITY_ID: &str = "entity_id";
 
 /// A notification that can be stored, associated with a given recipient.
 ///