docs: Add Mattermost as a notification provider and update related documentation

[hosseinmoghaddam]

• Included Mattermost in the list of supported notification providers in meta.json.
• Updated overview.mdx to describe Mattermost notifications.
• Created a new mattermost.mdx file with detailed setup instructions for Mattermost notifications.

Docs for Dokploy/dokploy#2728

Greptile Summary

Added Mattermost as a new notification provider with complete documentation including setup instructions, webhook configuration, and channel selection. The changes follow the existing documentation pattern used for other notification providers like Slack and Discord.

• Added mattermost.mdx documentation file with setup instructions
• Updated meta.json to include Mattermost in the navigation
• Updated overview.mdx to list Mattermost as a supported provider

Issues found:

• Duplicate step numbering in both mattermost.mdx (step 7 appears twice) and overview.mdx (item 8 appears twice)
• Grammar errors: "For start receiving" should be "To start receiving", and "a open source" should be "an open source"

Confidence Score: 4/5

• This PR is safe to merge after fixing the minor syntax and numbering issues
• The PR correctly implements documentation for a new notification provider following existing patterns. The only issues are minor syntax errors (duplicate step numbering and grammar mistakes) that should be fixed before merging. No logical errors or security concerns.
• All files have minor syntax issues that need correction before merging

_{Last reviewed commit: 579c69c}

_{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!}

[greptile-apps]

_{3 files reviewed, 4 comments}

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[Copilot]

Pull request overview

This pull request adds Mattermost as a new notification provider to Dokploy's documentation, including it alongside other supported providers like Slack, Discord, and Telegram.

Changes:

• Added Mattermost to the list of supported notification providers in the overview documentation
• Created comprehensive setup documentation for Mattermost notifications with webhook configuration steps
• Updated the navigation metadata to include the new Mattermost documentation page

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
apps/docs/content/docs/core/(Notifications)/meta.json	Added "mattermost" to the pages array after "slack" to include it in the documentation navigation
apps/docs/content/docs/core/(Notifications)/overview.mdx	Added Mattermost as the second provider in the list with a description, and renumbered subsequent providers
apps/docs/content/docs/core/(Notifications)/mattermost.mdx	New documentation file with setup instructions for configuring Mattermost webhook notifications, following the established documentation structure

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