docs release v1.8.7

• Add information about the gsctl delete endpoint command (https://github.com/giantswarm/docs/pull/495)
• Improve the sticky sidebar active section highlighting (https://github.com/giantswarm/docs/pull/496)
• Use ConfigMap everywhere instead of other variants, for consistency (https://github.com/giantswarm/docs/pull/498)
• Deprecate gsctl version command in favour of gsctl --version (https://github.com/giantswarm/docs/pull/499)