[mbed-tls] Mbed TLS long term support release plans

Hi,

Mbed TLS 2.16 LTS is approaching the end of its support period – it was originally announced that it would be maintained for at least 3 years up until the end of 2021 – and currently there is no other LTS branch.

To ensure that there is no period of time without a supported LTS branch, we plan to release 2.28 LTS in the near future (which will have the usual 3 year support period). We will continue supporting 2.16 LTS until this is available. The expectation is that as 2.28 will be API-compatible with 2.16, users of 2.16 LTS will be able to upgrade to 2.28 very easily.

Progress towards 2.28 LTS can be followed here: https://github.com/orgs/ARMmbed/projects/18#column-15836286

Dave Rodgman