Ability to suppress embeds

[heimskr]

This change adds the ability to suppress embeds in a message from another user through a combination of dpp::message::suppress_embeds(bool) and dpp::cluster::message_edit_flags.

Code change checklist

• [x] I have ensured that all methods and functions are fully documented using doxygen style comments.
• [x] My code follows the coding style guide.
• [x] I tested that my change works before raising the PR.
• [x] I have ensured that I did not break any existing API calls.
• [x] I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

[CLAassistant]

All committers have signed the CLA.

[github-actions[bot]]

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