fix(tools/docker): set esp-idf repo as safe directory

In our docker docs[1] we recommend to start docker as a non-root user. This has
a side effect, because the esp-idf repo in docker image is owned by
root. Git by default refuses even to parse a config file if the repo is
owned by other than current user. As a result the version detection in
cmake fails[2] and the app version is set to "HEAD-HASH-NOTFOUND".
This adds esp-idf repo to the system git config as a safe one.

[1] https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/
    tools/idf-docker-image.html#building-a-project-with-cmake
[2] espressif#12389 (comment)

Closes espressif#12389

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/docker/Dockerfile

@@ -68,6 +68,7 @@ RUN echo IDF_CHECKOUT_REF=$IDF_CHECKOUT_REF IDF_CLONE_BRANCH_OR_TAG=$IDF_CLONE_B
       ${IDF_CLONE_SHALLOW:+--depth=1 --shallow-submodules} \
       ${IDF_CLONE_BRANCH_OR_TAG:+-b $IDF_CLONE_BRANCH_OR_TAG} \
       $IDF_CLONE_URL $IDF_PATH && \
+    git config --system --add safe.directory $IDF_PATH && \
     if [ -n "$IDF_CHECKOUT_REF" ]; then \
       cd $IDF_PATH && \
       if [ -n "$IDF_CLONE_SHALLOW" ]; then \