Fix broken monitors link in README

[Copilot]

The Metrics section linked to a non-existent monitors repository, resulting in an empty search page when clicked.

Changes:

• Removed broken link to github.com/go-co-op?q=-monitor
• Restructured the Metrics section to provide separate documentation for each monitor type
• Added dedicated Implementations sections for Monitor, MonitorStatus, and SchedulerMonitor interfaces
• Each section clarifies that no OSS implementations currently exist and encourages community contributions
• Provided links to interface documentation and Slack channel for support
• Aligned formatting with existing Implementations sections (electors, lockers)

Before:

- [**Monitor**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#Monitor):
- [**MonitorStatus**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#MonitorStatus) (includes status and error (if any) of the Job)
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!)
- [**SchedulerMonitor**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#SchedulerMonitor):
A scheduler monitor provides comprehensive observability into scheduler and job lifecycle events.

After:

- [**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: There are currently no open source implementations of the Monitor interface available.
    We'd love for you to be the first to contribute one! Check out the [Monitor interface documentation](https://pkg.go.dev/github.com/go-co-op/gocron/v2#Monitor)
    to get started, or reach out on [Slack](https://gophers.slack.com/archives/CQ7T0T1FW) if you'd like to discuss your implementation.
- [**MonitorStatus**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#MonitorStatus):
Extends Monitor with status and error tracking for each job.
  - Implementations: There are currently no open source implementations of the MonitorStatus interface available.
    We'd love for you to be the first to contribute one! Check out the [MonitorStatus interface documentation](https://pkg.go.dev/github.com/go-co-op/gocron/v2#MonitorStatus)
    to get started, or reach out on [Slack](https://gophers.slack.com/archives/CQ7T0T1FW) if you'd like to discuss your implementation.
- [**SchedulerMonitor**](https://pkg.go.dev/github.com/go-co-op/gocron/v2#SchedulerMonitor):
A scheduler monitor provides comprehensive observability into scheduler and job lifecycle events.
  [... detailed metrics documentation ...]
  - Implementations: There are currently no open source implementations of the SchedulerMonitor interface available.
    We'd love for you to be the first to contribute one! Check out the [SchedulerMonitor interface documentation](https://pkg.go.dev/github.com/go-co-op/gocron/v2#SchedulerMonitor)
    to get started, or reach out on [Slack](https://gophers.slack.com/archives/CQ7T0T1FW) if you'd like to discuss your implementation.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[BUG] - README have a broken link to "monitors"</issue_title>
<issue_description>### Describe the bug

Under Metrics: https://github.com/go-co-op/gocron/?tab=readme-ov-file#metrics

There's a reference to "go-co-op monitors", but the link leads to the list of repositories under the org, where there are no "monitors" repo.

</issue_description>

<agent_instructions>Please update the Monitors section of the readme to reflect that there are not any OSS implementations of the gocron monitor interface yet, and suggest to the reader that they could be the first one to contribute one!</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@JohnRoesler hey @ptxmac thanks for reporting. As of today, there are no OSS implementations of the Monitor interface or the SchedulerMonitor. @JohnRoesler Yeah, agree, it needs some updating!

• Fixes [BUG] - README have a broken link to "monitors" #902

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[JohnRoesler]

@copilot Please add an implementations section here for SchedulerMonitor, similar to what you added for MonitorStatus. Also, please add an implementation section for the Monitor bullet above MonitorStatus

[Copilot]

Added separate Implementations sections for Monitor, MonitorStatus, and SchedulerMonitor. Each now has its own dedicated section with links to their respective documentation and Slack for support. (commit 5c73ecc)