Add Dockerimage for tgs conversion (#1211)

* Add Dockerfile with tgs to png conversion support

* Add .dockerignore to keep cache busts while testing low

.dockerignore

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+Dockerfile
+tgs.Dockerfile

tgs.Dockerfile

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+FROM alpine:edge AS builder
+
+COPY . /go/src/github.com/42wim/matterbridge
+RUN apk add \
+    go \
+    git \
+    gcc \
+    musl-dev \
+  && cd /go/src/github.com/42wim/matterbridge \
+  && export GOPATH=/go \
+  && go get \
+  && go build -x -ldflags "-X main.githash=$(git log --pretty=format:'%h' -n 1)" -o /bin/matterbridge
+
+FROM alpine:edge
+RUN apk --no-cache add \
+    ca-certificates \
+    cairo \
+    libjpeg-turbo \
+    mailcap \
+    py3-webencodings \
+    python3 \
+  && apk --no-cache add --virtual .compile \
+    gcc \
+    libffi-dev \
+    libjpeg-turbo-dev \
+    musl-dev \
+    py3-pip \
+    py3-wheel \
+    python3-dev \
+    zlib-dev \
+  && pip3 install --no-cache-dir lottie[PNG] \
+  && apk --no-cache del .compile
+
+COPY --from=builder /bin/matterbridge /bin/matterbridge
+RUN mkdir /etc/matterbridge \
+  && touch /etc/matterbridge/matterbridge.toml \
+  && ln -sf /matterbridge.toml /etc/matterbridge/matterbridge.toml
+ENTRYPOINT ["/bin/matterbridge", "-conf", "/etc/matterbridge/matterbridge.toml"]