feat(slack): Add option to include monitor group name in notifications

[dovansy1998]

Summary

In this pull request, the following changes are made:

Backend (server/notification-providers/slack.js)

• Added includeGroupName parameter to buildBlocks() method to conditionally display monitor group path in rich messages
• Implemented custom message templating support using Liquid templating (similar to Telegram notifications)
• Modified send() method to:
  • Support templating when slackUseTemplate is enabled
  • Include group name in plain text messages when slackIncludeGroupName is enabled
  • Display group path as italicized context in rich messages when enabled

Frontend (src/components/notifications/Slack.vue)

• Added checkbox toggle for "Include monitor group name" option
• Added checkbox toggle for "Use custom message template" option
• Integrated TemplatedTextarea component for template editing
• Added computed property for template placeholder with example

Resolves #6467

Details

### Please follow this checklist to avoid unnecessary back and forth (click to expand)

• ⚠️ If there are Breaking change (a fix or feature that alters existing functionality in a way that could cause issues) I have called them out
• 🧠 I have disclosed any use of LLMs/AI in this contribution and reviewed all generated content.
• I understand that I am responsible for and able to explain every line of code I submit.
• 🔍 Any UI changes adhere to visual style of this project.
• 🛠️ I have self-reviewed and self-tested my code to ensure it works as expected.
• 📝 I have commented my code, especially in hard-to-understand areas (e.g., using JSDoc for methods).
• 🤖 I added or updated automated tests where appropriate.
• 📄 Documentation updates are included (if applicable).
• 🧰 Dependency updates are listed and explained.
• ⚠️ CI passes and is green.

Screenshots for Visual Changes

• Before

• After

[github-actions]

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[dovansy1998]

@imclint21.
Can you review PR #6835 ?

[CommanderStorm]

LGTM with one change to how this defaults.

Please post screenshots of how these features interact so that I am sure that you have tested all combinations 😉

I think these are the code paths that are relevant:

• rich messages true/false + groups true/false + templates false (=> 4 screenshots)
• templates true (=> one additional screenshot)

[CommanderStorm]

Suggested change

	buildBlocks(baseURL, monitorJSON, heartbeatJSON, title, msg, includeGroupName = false) {
	buildBlocks(baseURL, monitorJSON, heartbeatJSON, title, msg, includeGroupName) {

[CommanderStorm]

Previous default.
Please also default this way on the frontend.

Suggested change

	const includeGroupName = notification.slackIncludeGroupName || false;
	const includeGroupName = notification.slackIncludeGroupName || true;

[dovansy1998]

rich messages true + groups true + templates false

rich messages true + groups false + templates false

rich messages false + groups true + templates false

rich messages false + groups false + templates false

templates true

[dovansy1998]

Hi, @CommanderStorm.
I posted screenshots on comment and updated code with suggesting fix.
Please review again.

[CommanderStorm]

Not sure why this is done this way.
I think you mean this, right?

Suggested change

	const includeGroupName =
	notification.slackIncludeGroupName === true || notification.slackIncludeGroupName === "true";
	const includeGroupName = notification.slackIncludeGroupName ?? true;

Also, please set this default in the frontend.
To do this, check how other notification providers do this in the mounted hook.

[CommanderStorm]

LGTM

[github-actions]

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