Update image blocks to allow links

[RachellCalhoun]

We want to

• add optional link to any block with an image. We can probably use URLBlock (https://docs.wagtail.org/en/latest/reference/streamfield/blocks.html#wagtail.blocks.URLBlock)
• update image template to include link if one exists
• make sure formatting will work with various images (rect/square)

One example:
RightImageLeftTextBlock https://github.com/djangonaut-space/wagtail-indymeet/blob/develop/home/blocks.py#L109-L118
template: https://github.com/djangonaut-space/wagtail-indymeet/blob/develop/indymeet/templates/blocks/right-image-left-text.html

To see these changes reflected you will need to make migrations, migrate, then you can create a new page (GeneralPage) and select the updated block and you should get a link option.

[RachellCalhoun]

The main driver for this was the sponsors -- but maybe we use the cards above, or create a logo block. It depends on how we want to display it. I think having a logo block would be helpful. https://tailwindcomponents.com/component/tailwind-css-logo-area-with-title