lavamind has been trying to get lektor_markdown_image_attrs to actually play nicely with our `packages` directory !73. because the plugin uses the hatch build system, it doesn't have a setup.py file and pip won't install it. the solution is to build a source distribution and to have pip install that. the problem is that `lektor plugins reinstall` doesn't install the source distribution by default. running `pip install package/*` works great, but it's not currently part of our CI flow, or our documentation. which brings us to the point of this ticket: agreeing on a way to install this new package since our current method doesn't work --- we've decided on using a requirements.txt file in each repository to manage dependencies. the next steps are: 1. [x] move lektor-requirements.txt from tpo/tpa/ci-templates to tpo/web/lego 2. [x] update lego everywhere 4. [x] set ci builds to install `lego/lektor-requirements.txt` and `requirements.txt` (if it exists) 3. [x] add a requirements.txt file to any lektor repo that uses additional packages 5. [x] add lektor_markdown_image_attrs as a dependency in `lego/lektor-requirements.txt`