feat: robyn_response()'s plot labels improvement

[laresbernardo]

• fix: It seems there's an issue on counting the periods in some cases. When testing c("2022-06-01", "2023-05-01") for example, I get 2 periods, which is incorrect. (See below)
• feat: adding total input and calculation results in caption when date range or metric value are provided into robyn_response().
• feat: for further clarification, added time granularity in x axis and dep variable in y axis.

PENDING BEFORE MERGING:

• Strange results are showing up sometimes. When metric_value = 0, I see the blue dot is larger than the grey dot, which is historical - which doesn't make sense. Maybe fixing the prior point fixes this as well. (See below)
• When using the date_range with narrower date range and NULL ("all"), I'm getting the same grey dot data in subtitle.
• What's the difference between sum(resp$input_total) and metric_value? @gufengzhou

[laresbernardo]

Example of metric_value = 0 result.

Example of metric_value = NULL result.