Add Agda to languages.yaml

[Zoltan-Balazs]

Adds support for Agda
Logo based on the official logo of Agda: https://agda.readthedocs.io/en/latest/_images/agda.svg

Improves #490

[o2sh]

Thanks for your contribution @Zoltan-Balazs

Here is a suggestion for a cleaner design:

Agda:
  type: programming
  ascii: |
    {0}   / / /           /  /
    {0}  / / /           /  / /
    {0} / o o           /    / /
    {0}/____           /      /
    {0}     |                 |
    {0}     |                 |
    {0}     ;                 ;
    {0}      \               /
    {0}       '.           .'
    {0}         '-._____.-'
  colors:
    ansi:
      - white
    chip: "#315665"

[Zoltan-Balazs]

Thank you for your feedback, I think that definitely looks cleaner!