Add Kubecon EU banner ads

[cjyabraham]

Updated ad listing is here.

• CNCF homepage hero takeover
  ?utm_source=www&utm_medium=homepage&utm_campaign=KubeCon-EU-2025&utm_content=hero

• CNCF hello bar for subpages and subsites
  ?utm_source=www&utm_medium=subpage&utm_campaign=KubeCon-EU-2025&utm_content=hello-bar

• CNCF big banner from Events infrastructure to appear on the CNCF.io homepage
  ?utm_source=www&utm_medium=homepage&utm_campaign=KubeCon-EU-2025&utm_content=big-banner

• Jobs sidebar ad; use this gist
  ?utm_source=jobs&utm_medium=homepage&utm_campaign=KubeCon-EU-2025&utm_content=sidebar-banner

• Community hello bar
  ?utm_source=community&utm_medium=homepage&utm_campaign=KubeCon-EU-2025&utm_content=hello-bar