Add optional attribute parameters to images inserted via %file()% command

[RealRaven2000]

The %file()% command can be used to insert inline images into the email. In order to better control styling and other aspects, allow adding attributes and values as parameters. For example:

%file(img/bargain-upg-bf-de.png,id=bargainStar,width=192)%

This should be converted by SmartTemplates reading the image as bitstream and append the attributes, like this:

<img
src="data:image/png;filename=bargain-upg-bf-de.png;base64,iVBORw0KGgoAAAAN...." id="bargainStar" width="192">

If a string is appended without the "=" then it will be regarded as the optional "alt" argument.

%file(img/bargain-upg-bf-de.png,id=bargainStar,"save 40 per cent")%

becomes this:

<img
src="data:image/png;filename=bargain-upg-bf-de.png;base64,iVBORw0KGgoAAAAN...." id="bargainStar" alt="save 40 per cent">

This makes it easy to add style rules to add more control over layout.

[RealRaven2000]

implemented in 3.15 released on 25/11/2022