🚥Add {index} variable starting with 0 to channel:entries in addition to {count}

[intoeetive]

Suggest an idea for ExpressionEngine

Within exp:channel:entries loop we have {count} variable which starts at 1.

Withing Grid however we also have {index} that starts with 0.

Sometimes it's useful to start counting with 0 (e.g. when using some javascript code in templates)

It would bring more consistency if we also add 0-started {index} to channel entries loop

[intoeetive]

#3795