ability to set git tag to download in external/pico_sdk_import.cmake

[ahmetkizilay]

it would be useful to lock the release/tag for projects that depends on the pico-sdk.

We can use PICO_SDK_FETCH_GIT_TAG to specify a release tag for the Pico SDK to download.

example usage:

set(PICO_SDK_FETCH_FROM_GIT true)
set(PICO_SDK_FETCH_FROM_GIT_TAG "1.5.1")
include(pico_sdk_import.cmake)

[peterharperuk]

I don't think we'd use it. master is always the latest release

[lurch]

I guess the implied usage-model here is for people who are copying pico_sdk_import.cmake into their own project, and want to pin to specific version of pico-sdk, so that their project doesn't get accidentally broken by later pico-sdk updates?

[peterharperuk]

That would make some sense I guess. Although isn't that what git submodules are for?