docs: add contributing md and update tooling/linting
Provides Makefile targets for tests and linting and uses these targets in the CI jobs. Also added vale to our .tool-versions
(markdownlint is installed via npm/yarn).
Added CONTRIBUTING.md
to begin documenting more development processes. Added linting details. Testing documentation will follow up from this MR.
Ensures docs linting runs for all our Markdown files, with the exception of .terraform local docs - closes #75 (closed).
Fixed various mardownlint and vale errors in the readme. This also required adjustment of GitLab relative links rule in this project to match absolute .md references rather than any project URLs.
Edited by Joe Shaw