Add inline action button sample with mm_blocks_actions

[sbishel]

Summary

• Add /inline_action slash command that posts a markdown issue-tracker table whose mmaction://triage?... links open a per-row triage dialog.
• Demonstrates the mm_blocks_actions post prop (with required type: "external") and per-click parameters carried in the link query string (id, title, priority, assignee) merged into the upstream URL by MergeQueryIntoURL. Static fields (project) still come through request.Context.
• Adds a /inline_action/triage HTTP handler that opens a follow-up dialog populated from those query params and the static context.

Ticket Link

Fixes https://mattermost.atlassian.net/browse/MM-68387

Test plan

• /inline_action posts the 5-row issue table.
• Clicking "Triage" on each row opens a dialog whose intro text shows that row's id / title / priority / assignee plus the static project=Demo Project.
• Submitting the triage dialog posts the standard "Dialog Submitted" message back to the channel.

Requires mattermost/mattermost#36219 to test.

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request adds an inline action feature to the Mattermost demo plugin. Users can invoke /demo_plugin inline_action to post a markdown table with an action button; clicking the button triggers an HTTP endpoint that opens an interactive triage dialog for issue management.

Changes

Inline Action Workflow

Layer / File(s)	Summary
Command trigger registration and dispatcher wiring server/command_hooks.go	Adds inline_action command constant, registers it with Mattermost command API with autocomplete and label, and routes the trigger in the ExecuteCommand dispatcher.
Command handler with action button server/command_hooks.go	Implements executeCommandInlineAction to build a markdown issue table post with mm_blocks_actions containing an external triage action pointing to the plugin's HTTP endpoint; logs and returns ephemeral error if post creation fails.
HTTP inline action triage endpoint server/http_hooks.go	Registers /inline_action/triage route and implements handleInlineActionTriage to parse triage metadata (id, title, priority, assignee, project), build an interactive dialog request, and open it via Mattermost API; includes formatJSON helper for indented JSON output.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: adding an inline action button sample that demonstrates the mm_blocks_actions feature.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The PR description clearly relates to the changeset, detailing the addition of an /inline_action slash command with markdown table posting and triage dialog functionality, matching the file changes in command_hooks.go and http_hooks.go.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch action_buttons

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@server/http_hooks.go`:
- Around line 517-525: The intro always prefixes assignee with '@', producing
"`@unassigned`"; change to build a display value that only prepends '@' for real
assignees. Create a local assigneeDisplay (or similar) based on assignee (e.g.,
if assignee == "unassigned" or empty then assigneeDisplay = "unassigned" else
assigneeDisplay = "@"+assignee) and use that in the fmt.Sprintf that builds
intro (referencing assignee, assigneeDisplay, and the existing fmt.Sprintf call
that builds intro using issueID, project, title, priority).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: e4cd24d6-f7ce-4326-be60-a3c0f70bf03a

📥 Commits

Reviewing files that changed from the base of the PR and between e9d7e1f and 47b0c4f.

📒 Files selected for processing (2)

• server/command_hooks.go
• server/http_hooks.go