Improve spacing for the banner

[msnassar]

There are some issues with the banner spacing:

• When there is no link added to the banner, the mb-4 on the description (p tag) is adding extra space.
  https://github.com/openeuropa/bootstrap-component-library/blob/development/src/compositions/bcl-banner/banner.html.twig#L87
  

• Also the p tag itself has margin.
  

Proposed resolution:

• Remove mb-4 from the description.
• Add new css rule to remove margin-bottom from p tag in bcl-banner
• Add margin top to link https://github.com/openeuropa/bootstrap-component-library/blob/development/src/compositions/bcl-banner/banner.html.twig#L90

[escuriola]

Hello @msnassar

A contribution would be welcome.

Regards