tools/docker: add IDF_CLONE_SHALLOW and IDF_INSTALL_TARGETS arguments

These two arguments can be used to reduce the size of the Docker
image:

- Setting IDF_CLONE_SHALLOW enables shallow cloning.
- Setting IDF_INSTALL_TARGETS to the comma separated list of targets
  results in toolchains being installed only for these targets.

tools/docker/Dockerfile

@@ -36,20 +36,26 @@ RUN python -m pip install --upgrade pip virtualenv
 # It is possibe to combine both, e.g.:
 #   IDF_CLONE_BRANCH_OR_TAG=release/vX.Y
 #   IDF_CHECKOUT_REF=<some commit on release/vX.Y branch>.
+# Use IDF_CLONE_SHALLOW=1 to peform shallow clone (i.e. --depth=1 --shallow-submodules)
 
 ARG IDF_CLONE_URL=https://github.com/espressif/esp-idf.git
 ARG IDF_CLONE_BRANCH_OR_TAG=master
 ARG IDF_CHECKOUT_REF=
+ARG IDF_CLONE_SHALLOW=
 
 ENV IDF_PATH=/opt/esp/idf
 ENV IDF_TOOLS_PATH=/opt/esp
 
 RUN echo IDF_CHECKOUT_REF=$IDF_CHECKOUT_REF IDF_CLONE_BRANCH_OR_TAG=$IDF_CLONE_BRANCH_OR_TAG && \
     git clone --recursive \
+      ${IDF_CLONE_SHALLOW:+--depth=1 --shallow-submodules} \
       ${IDF_CLONE_BRANCH_OR_TAG:+-b $IDF_CLONE_BRANCH_OR_TAG} \
       $IDF_CLONE_URL $IDF_PATH && \
     if [ -n "$IDF_CHECKOUT_REF" ]; then \
       cd $IDF_PATH && \
+      if [ -n "$IDF_CLONE_SHALLOW" ]; then \
+        git fetch origin --depth=1 --recurse-submodules ${IDF_CHECKOUT_REF}; \
+      fi && \
       git checkout $IDF_CHECKOUT_REF && \
       git submodule update --init --recursive; \
     fi