Add to OpenUPM

[msanatan]

I think I'll change the package name to Unity MCP, so it would appear like that via OpenUPM. And of course, update the README to encourage others to install it from there too

[msanatan]

Now we wait: openupm/openupm#5930

[msanatan]

Here we go! https://openupm.com/packages/com.coplaydev.unity-mcp/

[dsarno]

Hooray! Well done!