Add rpcCacheCapacity option to ApiOptions

[TarikGul]

The ApiPromise options (ApiOptions) now has support for rpcCacheCapacity. This will allow the ability to set the size of the cache in RpcCore.

interface ApiOptions extends RegisteredTypes {
  ...
  /**
   * @description Defines the size of the cache for the rpc-core. Defaults to 1024 * 10 * 10.
   */
  rpcCacheCapacity?: number;
  ...
}

This use to be infinite but for long standing instances where the api is used, this was terrible for memory, therefore we added an internal TTL for the LRUCache in #5997. But that PR also changed the storage cache for rpc calls from a Map to an LRUCache, which needs a defined size. This PR aims to allow the user to define an escape hatch to not have to deal with the default size.

[polkadot-js-bot]

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