CTA updates for top performing pages without clear CTA

A CTA audit showed we have some high pageview pages without a prominent CTA of any kind.

Added CTAs on:
/product/
/devops-tools/
/pricing/gitlab-com/feature-comparison/
/pricing/self-managed/feature-comparison/
/product/issueboard/

Updated CTAs on:
/solutions/kubernetes/
/features/

@brandon_lyon assigning to you since I added an include for /features/gitlab-pricing-trial.haml. Let me know if you see anything I can do to make this cleaner next time. Thanks!