llms.txt support

[YasharF]

Would you consider adding llms.txt to the documentation site?

It looks like there is a Vitepress plugin for it already: https://www.npmjs.com/package/vitepress-plugin-llms

This can help getting devops/etc AI tools to stick to the current version of the docs instead of relaying on their (potentially out of date) training data.

[slusarz]

vitepress-plugins-llms is unusable for us unless/until they fix okineadev/vitepress-plugin-llms#37 (vast quantities of Dovecot documentation are rendered as build-time data, so this is 100% required).

For Pro, we have https://doc.dovecotpro.com/main/datafiles.html, which includes a tar.gz of all files in markdown format. You can use that for CE as well. (There are no plans to implement this independently for CE.)