lua: merge encode_tagged into encode options

Encode_tagged is a workaround to be able to pass options to
yaml.encode().

Before the patch yaml.encode() in fact has this signature:
yaml.encode(...). So it was impossible to add any options to this
function - all of them would be treated as the parameters. But
documentation says: https://tarantool.io/en/doc/1.9/reference/reference_lua/yaml.html?highlight=yaml#lua-function.yaml.encode
that the function has this signature: yaml.encode(value).

I hope if anyone uses yaml.encode(), he does it according to the
documentation. And I can add the {tag_prefix, tag_handle} options
to yaml.encode() and remove yaml.encode_tagged() workaround.