commands(give): let users with ManageGuild permission self-run /give

[cotton105]

Allows users with the ManageGuild permission to run /give on themselves.

References

Fixes: #1077
Instead of requiring the Administrator permission, I have made it require the ManageGuild permission instead, to follow the userPermissions setting in the GiveCommand constructor.
I also ignored the issue requirement of allowing Bot Owner to run the command, because just the ManageGuild permission might be more appropriate.

Checklist

• Documentation is changed or added (if applicable)
• Commit message follows the commit guidelines

[atlanna]

Thank you for opening this pull request.
A maintainer will get by as soon as practical to review the changes.