Plotting functionality should join `historical_activity` to `ACT`

> @glatterf42 and @khaeru, I needed to filter the years explicitly here, because the plotting module does not show the values in historical years, which in this case is 690. Ideally, the plot should join `historical_activity` (for year 690) to `ACT` (for years 700, 710, and 720). If not possible, the plotting should not print historical year (690) without showing any value for that, which is the default behavior now.

_Originally posted by @behnam-zakeri in https://github.com/iiasa/message_ix/pull/815#discussion_r1553163224_

This was said with respect to [this line](https://github.com/iiasa/message_ix/pull/815/files#diff-9c16474c20e0255d0285ac8f8732949f08a0c9d5f2500f8084b5e49c2352d500R1366).

Start in the plotting module at the line referenced from pull request #815. Check how historical_activity for year 690 and ACT for years 700, 710, and 720 are selected and plotted. Done means historical year 690 is joined with its value, or omitted when no value can be shown.

Written by the indexing model from the issue text.