Add an instance limit to Config (#2593)

* Add an instance limit to `Config`

This commit adds a new parameter to `Config` which limits the number of
instances that can be created within a store connected to that `Config`.
The intention here is to provide a default safeguard against
module-linking modules that recursively create too many instances.

* Update crates/c-api/include/wasmtime.h

Co-authored-by: Peter Huene <peter@huene.dev>

Co-authored-by: Peter Huene <peter@huene.dev>

crates/c-api/src/config.rs

@@ -171,3 +171,8 @@ pub extern "C" fn wasmtime_config_static_memory_guard_size_set(c: &mut wasm_conf
 pub extern "C" fn wasmtime_config_dynamic_memory_guard_size_set(c: &mut wasm_config_t, size: u64) {
     c.config.dynamic_memory_guard_size(size);
 }
+
+#[no_mangle]
+pub extern "C" fn wasmtime_config_max_instances(c: &mut wasm_config_t, limit: usize) {
+    c.config.max_instances(limit);
+}