fix(api): add explicit futures-core dep to fix broken builds (#453)

This PR adds an explicit dependency to futures-core for `console-api` to
fix broken builds. Without this fix I get the following errors:

```
error[E0433]: failed to resolve: use of undeclared crate or module `futures_core`
   --> /home/weiznich/.cargo/registry/src/index.crates.io-6f17d22bba15001f/console-api-0.5.0/src/generated/rs.tokio.console.instrument.rs:275:34
    |
275 |         type WatchUpdatesStream: futures_core::Stream<
    |                                  ^^^^^^^^^^^^ use of undeclared crate or module `futures_core`

error[E0433]: failed to resolve: use of undeclared crate or module `futures_core`
   --> /home/weiznich/.cargo/registry/src/index.crates.io-6f17d22bba15001f/console-api-0.5.0/src/generated/rs.tokio.console.instrument.rs:289:38
    |
289 |         type WatchTaskDetailsStream: futures_core::Stream<
    |                                      ^^^^^^^^^^^^ use of undeclared crate or module `futures_core`

error[E0433]: failed to resolve: use of undeclared crate or module `futures_core`
   --> /home/weiznich/.cargo/registry/src/index.crates.io-6f17d22bba15001f/console-api-0.5.0/src/generated/rs.tokio.console.trace.rs:212:27
    |
212 |         type WatchStream: futures_core::Stream<
    |                           ^^^^^^^^^^^^ use of undeclared crate or module `futures_core`

```

The somewhat funny thing is that only happened after I've updated some
unrelated dependencies. It worked before, but after looking at the
relevant code I'm really surprised that it ever compiled without error.

console-api/Cargo.toml

@@ -37,6 +37,7 @@ tonic = { version = "0.9", default-features = false, features = [
 prost = "0.11"
 prost-types = "0.11"
 tracing-core = "0.1.17"
+futures-core = "0.3"
 
 [dev-dependencies]
 tonic-build = { version = "0.9", default-features = false, features = [