fix: update documentation and types for groupId (#384)

Relates to #380.

README.md

@@ -152,6 +152,7 @@ await fastify.register(import('@fastify/rate-limit'), {
 - `store`: a custom store to track requests and rates which allows you to use your own storage mechanism (using an RDBMS, MongoDB, etc.) as well as further customizing the logic used in calculating the rate limits. A simple example is provided below as well as a more detailed example using Knex.js can be found in the [`example/`](https://github.com/fastify/fastify-rate-limit/tree/master/example) folder
 - `skipOnError`: if `true` it will skip errors generated by the storage (e.g. redis not reachable).
 - `keyGenerator`: a sync or async function to generate a unique identifier for each incoming request. Defaults to `(request) => request.ip`, the IP is resolved by fastify using `request.connection.remoteAddress` or `request.headers['x-forwarded-for']` if [trustProxy](https://fastify.dev/docs/latest/Reference/Server/#trustproxy) option is enabled. Use it if you want to override this behavior
+- `groupId`: a string to group multiple routes together introducing separate per-group rate limit. This will be added on top of the result of `keyGenerator`.
 - `errorResponseBuilder`: a function to generate a custom response object. Defaults to `(request, context) => ({statusCode: 429, error: 'Too Many Requests', message: ``Rate limit exceeded, retry in ${context.after}``})`
 - `addHeadersOnExceeding`: define which headers should be added in the response when the limit is not reached. Defaults all the headers will be shown
 - `addHeaders`: define which headers should be added in the response when the limit is reached. Defaults all the headers will be shown

types/index.d.ts

@@ -118,6 +118,7 @@ declare namespace fastifyRateLimit {
     ban?: number;
     onBanReach?: (req: FastifyRequest, key: string) => void;
     keyGenerator?: (req: FastifyRequest) => string | number | Promise<string | number>;
+    groupId?: string;
     errorResponseBuilder?: (
       req: FastifyRequest,
       context: errorResponseBuilderContext

types/index.test-d.ts

@@ -41,6 +41,7 @@ const options1: RateLimitPluginOptions = {
   ban: 10,
   continueExceeding: false,
   keyGenerator: (req: FastifyRequest<RequestGenericInterface>) => req.ip,
+  groupId: '42',
   errorResponseBuilder: (
     req: FastifyRequest<RequestGenericInterface>,
     context: errorResponseBuilderContext