chore: set up release-please

[mdjermanovic]

Sets up release-please.

The release-please.yml file is copied from the eslint-visitors-keys repo. I only changed the package name in three places.

Additional non-code setup:

• Update organization Actions secrets to give this repository access to NPM_TOKEN, MASTODON_ACCESS_TOKEN and the four TWITTER_* secrets.
• Update repository Actions settings to "Allow GitHub Actions to create and approve pull requests". (this was already enabled!)
• Update npm package settings to "Require two-factor authentication or an automation or granular access token"

Please double-check the release-please.yml file and all non-code setup items.

[nzakas]

LGTM