Make plugin installable through hcli

[mrexodia]

Reference: https://hcli.docs.hex-rays.com/reference/packaging-your-existing-plugin

[emoose]

Looks useful, do you know if there's any examples of other loaders releasing with this? Had a look through and didn't actually see a way to specify this is a loader instead of a normal plugin, maybe HCLI handles that itself somehow though.