This switches from `markdownlint-cli` to `markdownlint-cli2` and drops
usage of the https://github.com/avto-dev/markdown-lint GitHub action in CI.

- The `avto-dev/markdown-lint` action was using a 4y old version of `markdownlint`.
  AFAICT that action is not being maintained.
- There is a new `npm run lint:markdown` and the `lint.yml` CI workflow uses it.
- The switch from `markdownlint-cli` to `markdownlint-cli2` and `.markdownlint-cli2.jsonc`
  as the config allows using the https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint
  VSCode plugin for in-editor Markdown lint warnings and intellisense in the config file.

Refs: open-telemetry/opentelemetry-js#4713

…les found by rule MD001 (see open-telemetry#2207)

…po disables this rule)

…CHANGELOG.md file and choose options that work for all .md files