Send one heartbeat on scheduling service startup anyway

[artem-shelkovnikov]

This PR makes connector service send a heartbeat for all configured connectors during heartbeat even if connector checked in recently.

This is done to be able to understand whether service has started or not from .elastic-connectors. This is helpful for migrations or general service monitoring (e.g. having deployment scripts or such that do deployment for connector service and then checking that connector is online).

Checklists

Pre-Review Checklist

• this PR does NOT contain credentials of any kind, such as API keys or username/passwords (double check config.yml.example)
• this PR has a meaningful title
• this PR links to all relevant github issues that it fixes or partially addresses
• if there is no GH issue, please create it. Each PR should have a link to an issue
• this PR has a thorough description
• Covered the changes with automated tests
• Tested the changes locally
• Added a label for each target release version (example: v7.13.2, v7.14.0, v8.0.0)

[navarone-feekery]

Nice one! 🚀

[github-actions]

💔 Failed to create backport PR(s)

The backport operation could not be completed due to the following error:
There are no branches to backport to. Aborting.

The backport PRs will be merged automatically after passing CI.

To backport manually run:
backport --pr 3014 --autoMerge --autoMergeMethod squash