doc: stm32: Update all st.com links to use HTTPS

While recent browsers seem to transparently try to use https for
http://www.st.com/... URLs, they are effectively not working anymore, so use
https://www.st.com/... URLs instead.

curl http://www.st.com/en/evaluation-tools/nucleo-g070rb.html

 -m 5 -v
*   Trying 104.89.117.48:80...
* Connected to www.st.com (104.89.117.48) port 80 (#0)
> GET /en/evaluation-tools/nucleo-g070rb.html HTTP/1.1
> Host: www.st.com
> User-Agent: curl/8.1.2
> Accept: */*
>
* Operation timed out after 5002 milliseconds with 0 bytes received
* Closing connection 0
curl: (28) Operation timed out after 5002 milliseconds with 0 bytes
received

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>