[5.0] Add parameter for setting template link color in dark mode

[wilsonge]

Fixes the accessibility of the links when in dark mode.

Summary of Changes

Adds a parameter to control the link color when in dark mode (this is a different color from the current one which doesn't meet a11y requirements).

I'll happily take any advice on how best to word both the label for the field and maybe even adding an option so it's clear. With us already talking "dark hue" and "dark text" it's really not that clear to the user what is going on (in my opinion)

Testing Instructions

Template link now accessible in dark mode to AA and controllable by the user in the template styles.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[brianteeman]

lgtm

[wilsonge]

OK I'll open it up then. Somehow I'm not sure this will be intuitive like I said. But better to at least allow a11y compliance

[HLeithner]

thanks