Add GitHub apps and generate tokens

[martonvago]

Configure GitHub following this guide:

• Install the auto-release-token and add-to-board-token GitHub Apps
• Create an UPDATE_VERSION_TOKEN and ADD_TO_BOARD_TOKEN secret for the GitHub Apps
• Create an UPDATE_VERSION_APP_ID and ADD_TO_BOARD_APP_ID variable of the GitHub Apps' IDs

[lwjohnst86]

Done 👍