Single Must Use Plugins Directory for local development

I have multiple local installations of WordPress and want to have a single Must Use Plugins directory for all my local sites.

Is there anything I can add to wp-config for instance that will let me have a single folder which can be used for all my sites? Or perhaps another approach?

For instance:

/root/sites/site1/…
/root/sites/site2/…
/root/sites/site3/…

all use:

/root/mu-plugins/

Thanks

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