docsgen: add versioning to flags

[Choraden]

Docsgen should allow to add oldest working version tag to flags.

Example from goreleaser

   # By default, GoReleaser will create your binaries inside
    # `dist/${BuildID}_${BuildTarget}`, which is a unique directory per build
    # target in the matrix.
    # You can set subdirs within that directory using the `binary` property.
    #
    # However, if for some reason you don't want that unique directory to be
    # created, you can set this property.
    # If you do, you are responsible for keeping different builds from
    # overriding each other.
    #
    # Templates: allowed (since v2.3). <---
    no_unique_dist_dir: true