Create github pages deploy for javadocs

[MinnDevelopment]

Pull Request Etiquette

• I have checked the PRs for upcoming features/bug fixes.
• I have read the contributing guidelines.

Changes

• Internal code
• Library interface (affecting end-user code)
• Documentation
• Other: _____

Closes Issue: NaN

Description

This adds a github action to deploy javadocs as github pages.

To use this the repository settings need to be updated:

1. Open Pages Settings
2. Set the source to GitHub Actions
   
3. Optionally configure a custom domain

This is one of the first steps towards independence from jenkins.

On push to master, this will deploy the updated documentation under dv8fromtheworld.github.io/JDA or on the custom domain. For example, my discord-webhooks project is hosted this way on https://minndevelopment.github.io/discord-webhooks/overview-tree.html

[Andre601]

I think the jda.wiki domain could be utilized here. Maybe jd.jda.wiki or docs.jda.wiki would be a good option (I personally would go with first option).
Alternatively use the dv8tion domain as it is used already for the Jenkins, but with a different subdomain.

[DV8FromTheWorld]

I like the concept of docs.jda.wiki
Is the only thing holding this back a merge and setting up the settings + domain?

Also, what happens to docs for other versions, like v4? Guess they just kinda die as we move?

[MinnDevelopment]

We will only have docs for the current master branch with this. However, older versions are available at javadoc.io.