Add menu to template that provides links to Apache pages

[jrudolph]

(courtesy of @pjfanning from https://github.com/apache/incubator-pekko/issues/92#issuecomment-1407728069):

• Apache home page
• Sponsoring
• License
• Trademark
• Security
• Thanks
• Upcoming Apache Event (a gif - or a link to a page)
• see the 'Apache Software Foundation' menu at top right of https://spark.apache.org/

[pjfanning]

@jrudolph I'm closing this as we have a solution. Please reopen if you think more work is needed.