Add job monitor interface to allow for collecting job metrics (#659)

* Add metrics each run of job

* Fix lint

* Fix test lint

* Fix backwards job status

* Add tags

* Comment example

* Rename it

* Fix some names

* Fix readme

* update readme, examples, naming

* fix unrelated test that was leaking scheduler

* remove overzealous leak detection

* rename interface methods

---------

Co-authored-by: gorodet-sky <gorodetsky.dev@gmail.com>

README.md

@@ -111,10 +111,12 @@ Multiple instances of gocron can be run.
 - [**Elector**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#WithDistributedElector):
 An elector can be used to elect a single instance of gocron to run as the primary with the
 other instances checking to see if a new leader needs to be elected.
-- Implementations: [go-co-op electors](https://github.com/go-co-op?q=-elector&type=all&language=&sort=)
+  - Implementations: [go-co-op electors](https://github.com/go-co-op?q=-elector&type=all&language=&sort=)
+    (don't see what you need? request on slack to get a repo created to contribute it!)
 - [**Locker**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#WithDistributedLocker):
 A locker can be used to lock each run of a job to a single instance of gocron.
-- Implementations: [go-co-op lockers](https://github.com/go-co-op?q=-lock&type=all&language=&sort=)
+  - Implementations: [go-co-op lockers](https://github.com/go-co-op?q=-lock&type=all&language=&sort=)
+    (don't see what you need? request on slack to get a repo created to contribute it!)
 
 ### Events
 Job events can trigger actions.
@@ -140,6 +142,13 @@ Logs can be enabled.
 The Logger interface can be implemented with your desired logging library.
 The provided NewLogger uses the standard library's log package.
 
+### Metrics
+Metrics may be collected from the execution of each job.
+- [**Monitor**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#Monitor):
+A monitor can be used to collect metrics for each job from a scheduler.
+  - Implementations: [go-co-op monitors](https://github.com/go-co-op?q=-monitor&type=all&language=&sort=)
+    (don't see what you need? request on slack to get a repo created to contribute it!)
+
 ### Testing
 The gocron library is set up to enable testing.
 - Mocks are provided in [the mock package](mocks) using [gomock](https://github.com/uber-go/mock).