[Feature request] Add a caption to sendMediaGroup

[mario-amazing]

SendMediaGroup don't have it's own caption parametr.
Solution is to add it to the first media as described here.

Current solution(add index caption under the hood):

respond_with :media_group, media: media_group

def media_group
  bot_session['files_ids'].map.with_index { |file_id, index| { type: 'photo', media: file_id }.merge(index == 0 ? { caption: t('.content') } : {}) }
end

Request Feature:

respond_with :media_group, media: media_group, caption: t('.content')

[printercu]

Thanks for figuring out the solution! These helpers were made as simple as possible to keep API concise yet extensible and also less opinionated. This makes it easier to support gem.

I've added similar method to the wiki. This method can be used like this:

respond_with :media_group, media: set_media_group_caption(media_group, t('.content'))