New delete_message_seconds parameter

[Middledot]

Summary

The delete_message_days parameter is deprecated and replaced with delete_message_seconds. discord-api-docs#5219

Shouldn't be merged until the docs get merged.

Information

• [ ] This PR fixes an issue.
• [x] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed).
• [ ] This PR is not a code change (e.g. documentation, README, typehinting, examples, ...).

Checklist

• [x] I have searched the open pull requests for duplicates.
• [x] If code changes were made then they have been tested.
  • [x] I have updated the documentation to reflect the changes.
• [ ] If type: ignore comments were used, a comment is also left explaining why.

[plun1331]

This is now officially documented - https://github.com/discord/discord-api-docs/commit/7e3e3a3de46a909c9a5bc04404f0df9a806e7271