[enh] Cache control on mjs files

[zamentur]

Problem

No cache on mjs files

Solution

Add simply mjs files to the location.
Note that the official doc use a tricks to manage in a better way the cache (we just have Expire 6M...
https://docs.nextcloud.com/server/latest/admin_manual/installation/nginx.html#nextcloud-in-a-subdir-of-the-nginx-webroot

PR Status

• Code finished and ready to be reviewed/tested
• The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[ericgaspar]

What preventing us to include this block?:

    include mime.types;
    types {
        text/javascript js mjs;
    }

[ericgaspar]

This should be fixed with #622