Discourse Rounded Image/Onebox borders

Meta topic: https://meta.discourse.org/t/rounded-image-onebox-borders/232044

Description

Created a very simple component to change the borders of images shown in topics.

Allows change of the following settings

• set rounding intensity
• set border width
• set border color
• set onebox rounding intensity
• change onebox border width
• change onebox border color
• change onebox background color

Light mode with 10px rounding and no border

Dark mode with 10px rounding and 2px border

Including onebox support