Add docker build for ESP32-C3

Notes:
* Currently builds against https://github.com/duncandrennan/esp-idf.git
  which has ESP-IDF v4.3.1 (latest stable release that supports ESP32-C3)
* rom.bin/elf are copied from esp32 folder and most likely not correct

tools/docker/esp32c3/Dockerfile-esp32c3-build

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+FROM ubuntu:bionic-20190807
+
+RUN DEBIAN_FRONTEND=noninteractive apt-get update && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y -q \
+      apt-utils autoconf bison build-essential flex gawk gdb-multiarch git gperf help2man \
+      libexpat-dev libncurses5-dev libtool-bin \
+      python python-dev python-git python-pyelftools python-serial python-six python-yaml \
+      python3 python3-dev python3-git python3-pyelftools python3-serial python3-six python3-yaml \
+      software-properties-common texinfo unzip wget zip && \
+    apt-get clean
+
+RUN cd /tmp && \
+    git clone https://github.com/rojer/fsync-stub && \
+    cd /tmp/fsync-stub && ./install.sh && \
+    rm -rf /tmp/fsync-stub
+
+RUN DEBIAN_FRONTEND=noninteractive apt-get install -y -q \
+      python-click python3-click \
+      python-cryptography python3-cryptography \
+      python-future python3-future \
+      python-pkg-resources python3-pkg-resources \
+      python-pyparsing python3-pyparsing \
+      python-setuptools python3-setuptools \
+      python-pip python3-pip \
+      rsync && \
+    apt-get clean
+
+RUN pip install reedsolo bitstring ecdsa
+
+RUN useradd -d /opt/Espressif -m -s /bin/bash user && chown -R user /opt
+
+ARG TOOLCHAIN_VERSION
+RUN cd /opt/Espressif && wget -q https://dl.espressif.com/dl/$TOOLCHAIN_VERSION.tar.gz && \
+    tar xzf $TOOLCHAIN_VERSION.tar.gz && \
+    rm $TOOLCHAIN_VERSION.tar.gz
+ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/Espressif/riscv32-esp-elf/bin
+ADD ct_path.sh /etc/profile.d
+
+ARG DOCKER_TAG
+RUN git clone -j 8 --branch $DOCKER_TAG --depth 1 --recursive --shallow-submodules https://github.com/duncandrennan/esp-idf.git /opt/Espressif/esp-idf
+RUN cd /opt/Espressif/esp-idf && git tag v$DOCKER_TAG
+ENV IDF_PATH=/opt/Espressif/esp-idf
+
+# Apply submodule patches.
+#RUN cd $IDF_PATH && ./patch_submodules.sh
+
+# Pre-build configuration tools
+RUN cd $IDF_PATH/tools/kconfig && make conf-idf
+
+ADD rom.bin rom.elf /opt/Espressif/rom/
+
+ADD mgos_fw_meta.py mklfs mkspiffs mkspiffs8 /usr/local/bin/
+ADD serve_core/ /opt/serve_core/
+RUN ln -s /opt/serve_core/serve_core.py /usr/local/bin/serve_core.py
+
+ARG DOCKER_TAG
+ENV MGOS_TARGET_GDB /opt/Espressif/riscv32-esp-elf/bin/riscv32-esp-elf-gdb
+ENV MGOS_SDK_REVISION $DOCKER_TAG
+ENV MGOS_SDK_BUILD_IMAGE docker.io/mgos/esp32c3-build:$DOCKER_TAG

tools/docker/esp32c3/Makefile

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+DOCKERFILES = esp32c3-build
+SPIFFS_CONFIG_PATH = /vfs-fs-spiffs/include/esp32
+TOOLCHAIN_VERSION = riscv32-esp-elf-gcc8_4_0-esp-2021r2-linux-amd64
+DOCKER_FLAGS = --build-arg=TOOLCHAIN_VERSION=$(TOOLCHAIN_VERSION) \
+               --build-arg=DOCKER_TAG=$(DOCKER_TAG)
+
+include ../docker.mk
+
+docker-pre-build-esp32c3-build: mgos_fw_meta.py serve_core mklfs mkspiffs mkspiffs8
+
+clean: clean-tools

tools/docker/esp32c3/ct_path.sh

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+export PATH="$PATH:/opt/Espressif/riscv32-esp-elf/bin"
+export SDK_PATH=/opt/Espressif/esp-idf