/xy command added and updated including !xy legacy command

[ManonLef]

Because

The !xy command needed an update and still didn't have an /xy slash command

This PR

• an /xy slash command is added
• !xy command is moved to its own file (used to reside in simpleCommands.js
• tests are added for the !xy command including snapshots
• tests were removed from simpleCommands.test.js file
• command output for both !xy and /xy are now an embed
• link in command output is updated to be a hyperlink with descriptive text
• /xy has an added non-mandatory option to ping a user

Current output:

This PR output:

Issue

Closes #429

Additional Information

Pull Request Requirements

• [x] I have thoroughly read and understand The Odin Project Contributing Guide
• [x] The title of this PR follows the location of change: brief description of change format, e.g. Callbacks command: Update verbiage
• [x] The Because section summarizes the reason for this PR
• [x] The This PR section has a bullet point list describing the changes in this PR
• [x] If this PR addresses an open issue, it is linked in the Issue section
• [x] If this PR adds new features or functionality, I have added new tests
• [x] If applicable, I have ensured all tests related to any command files included in this PR pass, and/or all snapshots are up to date