Add "KubeCon Amsterdam 2026" Banner to CLA Corp Console and Contributor Console

[mlehotskylf]

Add banners for Easy CLA & Corp CLA :

Text:
“Meet us in Amsterdam for KubeCon + CloudNativeCon Europe 2026 • Mar 23–26 •”

CTA Button:
“Register now”

CTA LINK for Corporate Console:
https://events.linuxfoundation.org/kubecon-cloudnativecon-europe/register/?utm_source=cla-corporate-console&utm_medium=homepage&utm_campaign=18269725-KubeCon-EU-2026&utm_content=hero

CTA LINK for Contributor Console:
https://events.linuxfoundation.org/kubecon-cloudnativecon-europe/register/?utm_source=cla-contributor-console&utm_medium=homepage&utm_campaign=18269725-KubeCon-EU-2026&utm_content=hero

This is pretty much the same as #4791, only location and date is different.