Display "firmware update available" when listing devices with available updates

**Is your feature request related to a problem? Please describe.**
Without this, we can get issues like in ARMmbed/mbed-os#4301

**Describe the solution you'd like**
Display a "firmware update available" message when the device's STLInk or DAPLink version is out of date.

We'd like to avoid hardcoding what the latest firmware available is. We'd also like to avoid hardcoding what "an update that contains a critical fix" is.

Possible sources of information about the latest DAPLink firmware versions available per board include: [The DAPLink website](https://armmbed.github.io/DAPLink/), [the DAPLink repo's release tags](https://github.com/ARMmbed/DAPLink/releases), or reading some file within a DAPLink release. Which version of DAPLink to use on which board may be board specific, but it might also be that any version will work.

We'll need to determine how to find the latest STLink version, too. For ST boards, all STLink versions are compatible with all boards (old boards never stop getting STLink firmware upgrades, even after they are deprecated or discontinued).

**Describe alternatives you've considered**
Display a warning about an STLInk or DAPLink version mismatch when there is an update available that is known to contain a critical fix.

**Additional context**
From @jeromecoutant:
"This is surely not the perfect place to do it, but this is my first proposition: https://github.com/ARMmbed/mbed-tools/commit/c4101506701355a10cb3b0159ab3071275ef7ec1"

Start by tracing the command that lists devices and determine how it reads STLInk or DAPLink versions. Research reliable sources for current board-compatible firmware, then define done as displaying “firmware update available” without hardcoded latest-version or critical-fix data.

Written by the indexing model from the issue text.