Update support policy link on konnect/availability-stages/

[TomKaweski]

Please update the link to Kong's support and maintenance policy on https://docs.konghq.com/konnect/availability-stages/ , which currently links to our April 2021 version, to the version available at the evergreen URL https://konghq.com/supportandmaintenancepolicy/

Here is the current text and link on the Docs website:

General availability
General availability, or GA, means that the software is released publicly and is supported according to Kong’s support and maintenance policy. Generally available features usually have official documentation (as needed) and interfaces are stable.

If feature documentation doesn’t have a tech preview, alpha, or beta label, then the feature is generally available.

You can depend on GA features in production environments.

[Guaris]

@TomKaweski This change has been made! Let us know if you need anything else.