Replace `yamllint` with `prettier`

[lengau]

Replace yamllint with prettier, as agreed by the team. This should include:

• lint-yaml Makefile target to lint yaml files with prettier (e.g. npx prettier --check snap/snapcraft.yaml)
• format-yaml Makefile target to format yaml files with prettier (e.g. npx prettier --write snap/snapcraft.yaml)
• Likewise for JSON files
• Likewise for Markdown files

Stretch goals:

• TOML: https://github.com/un-ts/toml-tools/tree/master/packages/prettier-plugin-toml

[syncronize-issues-to-jira[bot]]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-3626.

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