Scale cover image height on tipping banner

[dlipeles]

The cover image height on tipping banners is fixed at 176px leading to the cover image getting chopped.

Following discussion with @NejcZdovc and @jenn-rhim , it would be a good to fix the cover image rendering on the browser.

With a scaled height the banner could achieve something like

The solution would be dynamically calculating the height of the cover to (176/900) * width

[LaurenWags]

Verified passed with

Brave	0.69.124 Chromium: 76.0.3809.132 (Official Build) (64-bit)
Revision	fd1acc410994a7a68ac25bc77513d443f3130860-refs/branch-heads/3809@{#1035}
OS	Mac OS X

• Verified test plan from Don't vertically clip creator header images in tip UI brave-ui#484
• Encountered Tip banner text alignment is messed on default window size #5870 on a smaller sized window.
  custom image at ~1500px
  

custom image at ~1000px

standard image at ~1500px - verified image height is 176 px.

Verification passed on

Brave	0.69.130 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Ubuntu 18.04 LTS

• Verified test plan from Don't vertically clip creator header images in tip UI brave-ui#484
• Encountered Tip banner text alignment is messed on default window size #5870 on a smaller sized window.
  custom image at ~1500px
  

custom image at ~1000px

standard image at ~1500px - verified image height is 176 px.

Verification passed on

Brave	0.69.130 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Verified test plan from Don't vertically clip creator header images in tip UI brave-ui#484
• Encountered Tip banner text alignment is messed on default window size #5870 on a smaller sized window.
  custom image at ~1500px

custom image at ~1000px