feat: include pull request description in slack notifications

[rym-dd]

what

This PR aims to add the pull request description to the apply notifications sent through webhooks:

• add a Body field to models.PullRequest to carry the pull request description
• populate it in every event parser whose VCS payload exposes a description
• Bitbucket Cloud and Server are left empty on purpose, as their pull request payloads don't include a description
• render the description in the Slack apply notification as a full-width Description field, only when it's not empty, and rune-safe truncated to 1000 characters to stay within Slack's message size limits
• the HTTP webhook payload gains Body automatically since the whole ApplyResult is marshalled, so the payload example in the docs is updated to match

why

• apply notifications currently expose only the workspace, branch, user and directory, without any context about what was applied
• surfacing the pull request description gives the change, impact and environment context directly in the notification

tests

• added tests for createAttachments: the Description field is omitted when the body is empty, included when it's set, and rune-safe truncated when the body exceeds the limit
• extended the GitHub event parser tests (and fixture) to assert the body is parsed into PullRequest.Body
• make test passes in the ghcr.io/runatlantis/testing-env container, goimports and gofmt are clean, and golangci-lint reports no issues on the touched packages

before

after

references

• closes Add PR summary/body or additional info in slack webhook #3161

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR adds pull/merge request descriptions to Atlantis’ internal pull request model and surfaces them in Slack webhook notifications (with truncation), updating parsers, fixtures, tests, and docs accordingly.

Changes:

• Add Body to models.PullRequest and populate it in GitHub/GitLab/Azure DevOps/Gitea parsing.
• Include PR description as a Slack attachment field, truncating long descriptions rune-safely.
• Update test fixtures, parser tests, and docs to cover/reflect the new Body field.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
server/events/webhooks/slack_client.go	Adds PR description field to Slack attachments with truncation logic.
server/events/webhooks/slack_client_internal_test.go	Adds tests for presence/absence and truncation behavior of the Slack description field.
server/events/models/models.go	Introduces PullRequest.Body and documents its intended population behavior.
server/events/event_parser.go	Populates Body across supported VCS pull/merge request parsers.
server/events/event_parser_test.go	Updates/extends parser tests (incl. Gitea) to assert Body is parsed.
server/events/vcs/github/testdata/fixtures.go	Adds GitHub PR body to fixtures for parser tests.
server/events/vcs/azuredevops/testdata/fixtures.go	Adds Azure DevOps PR description to fixtures for parser tests.
runatlantis.io/docs/sending-notifications-via-webhooks.md	Documents Body in webhook payload example.

[chenrui333]

Thanks @rym-dd for your first contribution!

[demon]

Oh cool, you went with my suggestion :)