chore: adds Gitpod Flex support (#34916)

.devcontainer/Dockerfile

+FROM mcr.microsoft.com/vscode/devcontainers/base:ubuntu
+
+COPY package.json /tmp/package.json
+
+RUN apt-get update && apt-get install -y \
+    apt-transport-https \
+    build-essential \
+    ca-certificates \
+    curl \
+    jq \
+    libssl-dev && \
+    rm -rf /var/lib/apt/lists/*
+
+ENV NVM_DIR /usr/local/nvm
+RUN mkdir -p $NVM_DIR && \
+    curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash && \
+    bash -c ". $NVM_DIR/nvm.sh && nvm install $(jq -r '.engines.node' /tmp/package.json) && npm install -g yarn"
+
+RUN echo "export NVM_DIR=$NVM_DIR" >> /etc/bash.bashrc && \
+    echo "[ -s \"$NVM_DIR/nvm.sh\" ] && \. \"$NVM_DIR/nvm.sh\"" >> /etc/bash.bashrc
+
+ENV DENO_INSTALL=/usr/local/deno
+RUN mkdir -p $DENO_INSTALL && \
+    curl -fsSL https://deno.land/install.sh | sh
+
+ENV DENO_INSTALL="/usr/local/deno"
+ENV PATH="$DENO_INSTALL/bin:$PATH"
+
+RUN echo 'export DENO_INSTALL="/usr/local/deno"' >> /etc/bash.bashrc && \
+    echo 'export PATH="$DENO_INSTALL/bin:$PATH"' >> /etc/bash.bashrc
+
+ENV METEOR_INSTALL="/usr/local/meteor"
+ENV PATH="$METEOR_INSTALL/bin:$PATH"
+
+RUN curl https://install.meteor.com/ | sh && \
+    mv ~/.meteor $METEOR_INSTALL
+
+RUN echo 'export METEOR_INSTALL="/usr/local/meteor"' >> /etc/bash.bashrc && \
+    echo 'export PATH="$METEOR_INSTALL/bin:$PATH"' >> /etc/bash.bashrc
+
+CMD ["bash"]

.devcontainer/devcontainer.json

+{
+	"name": "Rocket.Chat Gitpod",
+	"build": {
+        "context": "..",
+        "dockerfile": "./Dockerfile"
+    },
+	"features": {
+        "ghcr.io/devcontainers/features/docker-in-docker:2": {}
+    },
+	"forwardPorts": [3000],
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"esbenp.prettier-vscode"
+			]
+		}
+	}
+}

.gitpod/automations.yaml

+services:
+  development-server:
+    name: Rocket.Chat development server
+    description: Starts the Rocket.Chat development server (yarn dsv)
+    triggeredBy:
+      - postDevcontainerStart
+      - manual
+    commands:
+      start: |
+        yarn
+        yarn dsv
+      ready: |
+        export ROOT_URL=$(gitpod environment port open 3000 --name "Rocket.Chat application" | sed 's|https://||')
+        echo $ROOT_URL
+        gitpod environment port open 3000 --name "Rocket.Chat application"