feat(plugins): add "how to" for plugin creation

Summary

• feat(plugins): add "how to" for plugin creation

Add first part with manifest, *.so build and migrations

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• References #239 (closed)
• Close #282 (closed)
• Cherry-pick to: none

https://docs.binary.picodata.io/picodata/dkoltsov_plugin_tutorial/tutorial/create_plugin/