This simplifies the impl by doing global on-attach logic in a
`LspAttach` autocmd instead of adding lua lines to each server's
individual `on_attach` callback.
This is effectively a `mkAliasOptionModule` alias, other than the alias
only being applied when `plugins.lsp.enable`.
This commit adds a `plugins.<name>.luaConfig` section controlling the
plugin specific configuration.
The section contains the internal `init` option, containing the plugin's
initialization code.
It also contains the public `pre` and `post` options, that allow to add
code before & after the `init` section
Finally, it contains the `final` option, being the concatenation of the
three previous options.
