Added prometheus metrics middleware. (#99)

Author: s3rius

docs/available-components/README.md

@@ -9,5 +9,6 @@ dir:
 In this section, you can find a list of officially supported plugins for the taskiq.
 
 - [Available brokers](./brokers.md)
+- [Available middlewares](./middlewares.md)
 - [Available result backends](./result-backends.md)
 - [Available schedule sources](./schedule-sources.md)

docs/available-components/middlewares.md

@@ -0,0 +1,69 @@
+---
+order: 5
+---
+
+# Available middlewares
+
+Middlewares allow you to execute code when specific event occurs.
+Taskiq has several default middlewares.
+
+### Simple retry middleware
+
+This middleware allows you to restart functions on errors. If exception was raised during task execution,
+the task would be resent with same parameters.
+
+To enable this middleware, add it to the list of middlewares for a broker.
+
+```python
+from taskiq import SimpleRetryMiddleware
+
+broker = ...
+
+broker.add_middlewares(SimpleRetryMiddleware(default_retry_count=3))
+```
+
+After that you can add a label to task that you want to restart on error.
+
+```python
+
+@broker.task(retry_on_error=True, max_retries=20)
+async def test():
+    raise Exception("AAAAA!")
+
+```
+
+`retry_on_error` enables retries for a task. `max_retries` is the maximum number of times,.
+
+### Prometheus middleware
+
+You can enable prometheus metrics for workers by adding PrometheusMiddleware.
+To do so, you need to install `prometheus_client` package or you can install metrics extras for taskiq.
+
+::: tabs
+
+
+@tab only prometheus
+
+```bash
+pip install "prometheus_client"
+```
+
+@tab taskiq with extras
+
+```bash
+pip install "taskiq[metrics]"
+```
+
+:::
+
+
+```python
+from taskiq import PrometheusMiddleware
+
+broker = ...
+
+broker.add_middlewares(PrometheusMiddleware(server_addr="0.0.0.0", server_port=9000))
+```
+
+After that, metrics will be available at port 9000. Of course, this parameter can be configured.
+If you have other metrics, they'll be shown as well.

docs/extending-taskiq/README.md

@@ -13,7 +13,7 @@ All abstract classes can be found in `taskiq.abc` package.
 ## Contents:
 
 - [Brokers](./broker.md)
-- [Brokers](./broker.md)
+- [Middlewares](./middleware.md)
 - [Result backends](./resutl-backend.md)
 - [CLI](./cli.md)
 - [Schedule sources](./schedule-sources.md)