Changing suggestion status should update the timestamp #565

1. Describe the bug

When a suggestion is posted, the timestamp is included in the footer of the embed.

When a suggestion is accepted, declined or put on hold by a moderator, the timestamp in the footer still displays the time when the suggestion was originally posted, not the decline/accept timestamp.

2. Steps to reproduce

• Setup: Make sure a suggestion channel ID is set in the guild config in moderationConfig.suggestionChannelId
• Send a message in the configured suggestion channel. The bot should delete it and replace it with an embed.
• Copy the ID of the message
• A user with the MODERATE_MEMBERS permission runs /suggestion accept with the message ID in the suggestion channel
• The timestamp is kept as-is

3. Expected behavior
   The message timestamp should be updated to the current timestamp.