Generate dockerfile in GHA

Dockerfile

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+# First stage
+FROM alpine:latest
+
+COPY . /src
+
+
+RUN apk add build-base wget git bash cmake python3 glu-dev
+
+# Installing SDL2 from source because current SDL2 package in alpine
+# has some tricks that make PPSSPP compilation to fail
+ENV SDL_VERSION=2.0.20
+RUN wget https://github.com/libsdl-org/SDL/archive/refs/tags/release-${SDL_VERSION}.tar.gz && \
+    tar -xf release-${SDL_VERSION}.tar.gz && cd SDL-release-${SDL_VERSION} && mkdir build && cd build && \
+    cmake -DCMAKE_BUILD_TYPE=Release .. && \
+    make -j$(getconf _NPROCESSORS_ONLN) clean && \
+    make -j$(getconf _NPROCESSORS_ONLN) && \
+    make -j$(getconf _NPROCESSORS_ONLN) install
+
+RUN cd src/ffmpeg && ./linux_x86-64.sh
+RUN cd src && ./b.sh --headless
+
+# Second stage
+FROM alpine:latest
+
+# Install required dependencies to make headless to work
+RUN apk add --no-cache sdl2 libstdc++ glu-dev
+
+# Copy minimal things to make headless to work
+COPY --from=0 src/build/PPSSPPHeadless usr/local/bin/
+
+RUN PPSSPPHeadless || true