Add online generation of mermaid graph

The implementation of mermaid in DiagrammeR is too old and I use to update the mermaidjs script manually in DiagrammeR in order to get the last version (See: https://github.com/rich-iannone/DiagrammeR/issues/475).

Using the mermaid.live website to generate graph and directly get PNG or SVG file can be done with links like: https://mermaid.ink/img/pako:eNqllFFuozAQhq-C_JRKNQfIQ6VGsG1XaURqHiKVFXLwEJDARrZpNqp6oD1HL1YbTNRWjtRk5wWw5_vHDD_zigrBAM1R2Yh9UVGpg-VTxoNgEUWzWUnnJcWMarqlCuza1ZXbDDC-sdc8eS6ptGmlaBhILDrg40Yw4kUjeoZVJfYgFa6AvhzC8M93mfiUTOxkVM89WHoKSx2moe1AUt1LwFW9qzwa61Maa6expxrkN87LUKVqrhzV0g43oqC6FhwzoYfKVkP1252kXRXcPSXPkeD8_R8o--D2x-bZKomJmStUiO4QbFzkSc75b87vOX8Mo9s0nD6LaZcFYxN-MD4FpgOYmvCD6af0sQUbf6JPfwDu_QCuDp0Sof6rx2Tg7NiHgftlWkN8_bbrrtm7RmzB22HypcVk-IqD4qB9t1kZZfVJWUsAz8vkKxOjBwwzsOQ_rH_UOMP3R-ZS05PEnfs8W5HYHfU8U5HUnfYnlprebbmYUsu6gWD5QNI4X9wS8rAiOYks8CWfXPojmvMtnMLPfTwhFzjZDBOLrk34y62nMugatSBbWjMzll8tniFdQQsZmptbBiXtG52hjL-ZVNprQQ68QHMte7hGfWfGNUQ1NT9Ai0yZRplVYLUW8nEc9cPEf_sAigjozg?type=png

The mermaid script is encoded in "pako" format. There is a python implementation on: https://github.com/mermaid-js/mermaid-live-editor/discussions/1291