[Feature] List existing ships

[SnowHawkeye]

Description

Implement the ability to list existing ships with /ships.
When using the command, a message appears. Each ship is displayed with the following information (single line everytime):

• type
• name
• rank
• timeRemaining if the ship was sent, or a message indicating it hasn't been sent (can be a placeholder until [Feature] Send a ship #21 is implemented)
• a button to see the ship's details ("details")

There might be limitations for button placement within messages (might not be able to put them on the same line as the text). In that case, simply have a "details" button at the bottom that does the same as /details (i.e. starts by asking which ship the user wants to see details for).

Acceptance criteria

• When using the command, an ephemeral message as described above appears
• Relevant documentation has been added

Note: The buttons don't have to work yet, they will be implemented in #22