Adds support for passing html attributes to svg templatetag

[jurecuhalev]

With inlining SVG's it's often useful to give them class names to support things like using CSS to change fill color. Another really useful approach is when using a framework like tailwind, that uses utility classes to be able to just say:

{% svg 'icon-search' class='h-10 mt-6' %}

and this will add fixed height and top margin to SVG.

This PR adds the ability to add extra attributes to the templatag.

This change is inspired by Log1x/sage-svg, that makes it really easy to use this pattern in Laravel Blade nad Sage Wordpress theme.

[igorms-pro]

wow I want something like that. Why this is not merged yet ?

[geoffbeier]

I checked the PRs hoping to see one that did exactly this. Thanks for putting it together. I'm now using your fork.