Added dev container

[dmccoystephenson]

Problem

Compiling the program requires having a number of dependencies installed at this time, which can be a barrier to entry for contributors.

Solution

A dev container has been added to the project. Now developers just need to install Docker and they should be able to compile with ease.

Testing

This has been tested locally with VSCode. Compiling the rpk-chat-bukkit module with the gradle wrapper has been verified to work.

Note

Attempting to compile the rpk-characters-bukkit module is resulting in an ambiguous method overload error at this time. I am not sure if this is due to the configuration of the dev container or if it is an actual problem that needs to be resolved across the board.

Relevant Issue

The changes in this PR resolve #664

[dmccoystephenson]

Marking this as a draft for now since the Kotlin Language Server VSCode extension is running into an error upon starting inside of the dev container. Relevant issue here: fwcd/kotlin-language-server#564

[dmccoystephenson]

Marking this as 'ready for review' again. The development container can be used to compile the program, which is sufficient for development. Although it would be preferable to have syntax highlighting within the container, this can be addressed in a future pull request. Developers have the option to use the Kotlin Language Server plugin locally and run the development container for compilation, or they can use IntelliJ.