[chronik.e.cash] Docs site for chronik

Summary: Docusaurus site for chronik ready to deploy (and preview) at chronik.e.cash

Test Plan:
Change line 25 of modules/Dockerfile to read ARG NGINX_CONF=nginx-preview.conf so that header settings specific to https are not present for test build

cd modules/
./build-docker
docker run --rm -p 8080:80 --name chronik-docs chronik-docs

Navigate to localhost:8080 and see working docs

• Confirm infra and teamcity deployments are configured before landing (ref D15768)

Reviewers: #bitcoin_abc, tobias_ruck, Fabien

Reviewed By: #bitcoin_abc, tobias_ruck, Fabien

Subscribers: Fabien, tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D15767