[feature] Use plugin mechanism to extend more data storage

[wjunLu]

What would you like to be added:

I would like to extend the unsupported data storage backends as plugins.

Why is this needed:

To use those unsupported data storage backends, one has to invasively modify the source code. If the extended backends can be used as plugins, it will not only reduce the workload of maintaining the code, but also make it easier to spread these extensions everywhere.

For example, docker has many extended plugins, such as docker-buildx for old version to support multi-platform build. I think plugin mechanism for juicefs will also bring users a more flexible function extension.