fix: change default plugin path

[Integral-Tech]

• According to FHS (Filesystem Hierarchy Standard):

The /etc hierarchy contains configuration files. A "configuration file" is a local file used to control the operation of a program; it must be static and cannot be an executable binary.

Therefore, plugins which are .so files shouldn't be placed in /etc. Instead, they should be placed in /usr/lib/anyrun/plugins.

[Integral-Tech]

Any progress on this pull request?

[Kirottu]

This will be fixed with the relm4 port.