Implement Storage#upload() request

[davispuh]

POST /api2/json/nodes/{node}/storage/{storage}/upload API allows to upload ISO images which can then be used for VM installation.
See https://pve.proxmox.com/pve-docs/api-viewer/index.html#/nodes/{node}/storage/{storage}/upload

This PR implements this API allowing to

storage = Fog::Storage.new(provider: :proxmox, **params)
isopath = 'my.iso'
file = File.open(isopath, 'rb')
storage.upload({
        node: node,
        storage: storage
    },
    {
        content: 'iso',
        file: file,
        filename: File.basename(isopath)
    }
)

[Manisha15]

Can you please fix the linting issue?

[davispuh]

Now it should be fixed

[davispuh]

I rebased this and test now passes but coverage step fails. I don't really understand that so maybe you could look into fixing that?

[Manisha15]

I rebased this and test now passes but coverage step fails. I don't really understand that so maybe you could look into fixing that?

Yes the coverage test failure is known issue and shouldn't affect PR merge.