Add Media Box to GitHub inline tipping banner

[jdkuki]

Description

When a tip button is clicked, it opens a dialog to tip the user. For Reddit and Twitter, a Media Box containing the post content is also in the banner. This should be added for GitHub.

cc @alexwykoff @jenn-rhim

Steps to Reproduce

Actual result:

N/A

Expected result:

(Equivalent for GitHub)

Reproduces how often:

Brave version (brave://version info)

Version/Channel Information:

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the dev channel?
• Can you reproduce this issue with the nightly channel?

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information: