[Heartbeat] Fix reload policy hash consistency, browser monitor cleanup and semaphore release

[emilioalvap]

What does this PR do?

Closes #34629.

Addresses multiple issues with private location updates:

• Remove global fields from policy to prevent agent from stopping integrations which have not been updated.
• Detect browser monitor has ben cancelled by having a global (to the monitor) context .
• Fix an issue where job limit semaphore was not released after being acquired.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

1. Create a private location policy with multiple long-running browser monitors.

step("Test", async () => {
    await page.goto("https://google.es");
    await page.waitForTimeout(600e3);
})

2. Enroll an agent in the policy.
3. On a different window, monitor processes executed by agent-heartbeat. This is an example to monitor a docker instance:

$: docker exec -it -u root agent watch ps -aef

4. Start updating monitors in Kibana (can be by enabling/disabling them) one by one and watch for agent reaction.
   • When a monitor that is running is disabled, heartbeat should kill the synthetics process and schedule the next job.
   • When a monitor that is not running is updated, heartbeat should not terminate any of the running jobs.
   • After multiple updates, heartbeat should still continue scheduling jobs since the job limit semaphore is updated even when a job is cancelled.

[elasticmachine]

Pinging @elastic/uptime (Team:Uptime)

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @emilioalvap? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

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• Start Time: 2023-03-07T15:38:38.132+0000

• Duration: 48 min 12 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1921
Skipped	25
Total	1946

💚 Flaky test report

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[andrewvc]

LGTM, confirmed with local testing