Implement /find_members Command

[Heixier]

Issue Title: Implement "/find_members" Command

Issue Description: As a user of our Discord bot, I want to be able to use a "/find_members" command to list all member names that match a certain string in order to visually sort them.

Feature Description:

• The "/find_members" command should take one required option: the text to search for, and one optional choice: whether to query members using nickname or displayName. By default, it will query using nickname.
• The bot should validate the string to ensure it is not empty (so it doesn't list everyone in the server).
• An appropriate error message should be displayed if the string is empty, and if no results are found.
• The bot will respond with a mentioned list of every user with the matching string in their nickname or displayName without pinging them.
• The bot will display the search query in its response.
• The bot's response will be properly formatted (concise, neat, and easy to read).

Acceptance Criteria:

• The "/find_members" command is successfully implemented and tested.
• Invoking the "/find_members" command with a valid string should return a mentioned list of every user.
• These users must be mentioned but not pinged.
• If the input is invalid or no matches were found, appropriate error messages are returned.
• The bot displays the search query in its response, and the response has to be concise, neat, and easily-readable.

Additional Notes:

• This feature will enhance the functionality of our Discord bot by allowing users to display filtered members in chat.
• Please ensure thorough testing of the "/find_members" command functionality before closing this issue.
• Make sure the output is as readable as possible. You may use creative formats such as EmbedBuilder to make the output more readable.

[Heixier]

This is actually M/L depending on whether you use EmbedBuilder or similar to format your output. Without the requirement for good formatting, this would be an M instead