Add support for having the target subtitles to be a function

[dianabarsan]

Is your feature request related to a problem? Please describe.
Frequently, the target subtitle_translation_key translation is related to the target reporting period, but this is not necessarily true. When wanting to show targets for previous months, this subtitle value needs to change and respond to the reporting interval displayed.

Describe the solution you'd like
Add support for the target subtitle_translation_key to be a function, that receives a parameter for the calendar interval that is being displayed.

[Edwin-Rugoogamu]

looking at it

[Edwin-Rugoogamu]

hi @dianabarsan Please have a look at this PR.

medic/cht-core#10507

The function is being defined in the html file . It defermines when the subtitle (This Month or All Time ) according to the time period selected. Please have a look . Looking forward to any changes or enhacements we to be adjusted.

[Edwin-Rugoogamu]

hi @dianabarsan Please have a look at the new PR

medic/cht-core#10507

The function has been created and adjusted in regards to the advice you provided. Please have a look . Looking forward to your reply.