fix(Discord): Move message content to embed description field

[chernistry]

What this PR does

Fixes the Discord notification formatting where the alert message text appears above the embed title instead of below it.

The root cause is that the v1 Discord notifier places the message in the webhook's top-level content field, which Discord renders above all embeds. The fix moves the message to the embed's description field, which renders below the title within the embed -- matching the behavior of Slack and other notification channels.

Changes

• Added Description field to discordLinkEmbed struct
• Message content is now placed in linkEmbed.Description instead of msg.Content
• Truncation limit updated from 2000 (content field limit) to 4096 (embed description limit per Discord docs)
• Tests updated to reflect the new payload structure

Before

[Message content appears here, above the embed]
┌─────────────────────────┐
│ Title                   │
│ Footer                  │
└─────────────────────────┘

After

┌─────────────────────────┐
│ Title                   │
│ Message content here    │
│ Footer                  │
└─────────────────────────┘

Note: The v0mimir1 Discord notifier already uses Description correctly. This fix aligns v1 with the same pattern.

Which issue(s) this PR fixes

Fixes grafana/grafana#86565

Checklist

• Tests updated and passing
• Follows existing code patterns (matches v0mimir1 behavior)

---

Note

Medium Risk
Moderate risk because it changes the Discord webhook payload structure and truncation limits, which can affect message rendering and any consumers expecting content to be populated.

Overview
Discord v1 notifications now render the alert message inside the embed by adding an embed description field and populating it with the templated message, leaving top-level content empty so text no longer appears above the title.

Message truncation is updated to Discord’s embed description limit (4096 runes), and tests are adjusted (including image/embedded quota cases) to assert the new payload shape and truncation behavior.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

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Embed total may exceed Discord's 6000 character limit

Medium Severity

Moving the message from the top-level content field (which doesn't count toward embed limits) into the embed Description field (which does) means the message text now contributes to Discord's 6000-character total across all embeds. With discordMaxDescriptionLen at 4096, plus discordMaxTitleLen at 256, footer text, and up to 9 image embed titles (each up to 256 chars), the theoretical maximum is ~6681 characters — exceeding 6000. Discord will reject such messages. Previously, the content field was outside embeds so this limit couldn't be hit.

Additional Locations (1)

• receivers/discord/v1/discord.go#L169-L187

 

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