Migrate from CircleCI to GitHub Actions

[simskij]

resolves #11

Requires the following environment variables to be set up to work.

STAGING_CI_ALGOLIA_ADMIN_KEY
STAGING_CI_AWS_ACCESS_KEY
STAGING_CI_AWS_CLOUDFRONT_DISTRIBUTION_ID
STAGING_CI_AWS_SECRET_KEY
STAGING_CI_BUCKET_NAME
STAGING_CI_BUCKET_REGION
STAGING_CI_GATSBY_ALGOLIA_APP_ID
STAGING_CI_GATSBY_ALGOLIA_INDEX_NAME
STAGING_CI_GATSBY_ALGOLIA_SEARCH_ONLY_KEY
STAGING_CI_MAIN_URL
STAGING_CI_GATSBY_DRIFT_API
STAGING_CI_GATSBY_GOOGLE_API_KEY

Have only been able to test this to a small degree as the env vars are missing. However, until we actually create a tag, it will only affect staging, so should be safe to merge once the env vars have been set up.

Once we switch to this CI pipeline, all pushes to master will be published to staging, while any tags matching the regex v.* will publish to production.

Also:

• Includes fixes for all linting errors in the whole repo, as our current husky lint hook only lints staged files.
• Enables full code lining as part of the CI workflow.
• Enables prose linting as part of the CI workflow.

[ppcano]

@bolotskydev please, could you review this.

@simskij can you share the instructions to release to production? Perhaps, providing a command is the best.

[bolotskydev]

lgtm 👌