plugin: fix InstallPlugin() API by manually creating RPC code (#13041)

Flugin: fix InstallPlugin() API by manually creating RPC code

previous implementation of InstallPlugin()-#12232 's RPC funcs wasn't working because `io.Reader` isn't supported by the RPC code generation tool.

RPC does not support streaming data and RPC code generation tool does not handle this exception.

thus, RPC funcs are now implemented manually to stream `io.Reader` through a separate multiplexed connection.

plugin/client_rpc_generated.go

@@ -8,7 +8,6 @@ package plugin
 
 import (
 	"fmt"
-	"io"
 	"log"
 
 	"github.com/mattermost/mattermost-server/v5/mlog"
@@ -3607,36 +3606,6 @@ func (s *apiRPCServer) GetPluginStatus(args *Z_GetPluginStatusArgs, returns *Z_G
 	return nil
 }
 
-type Z_InstallPluginArgs struct {
-	A io.Reader
-	B bool
-}
-
-type Z_InstallPluginReturns struct {
-	A *model.Manifest
-	B *model.AppError
-}
-
-func (g *apiRPCClient) InstallPlugin(file io.Reader, replace bool) (*model.Manifest, *model.AppError) {
-	_args := &Z_InstallPluginArgs{file, replace}
-	_returns := &Z_InstallPluginReturns{}
-	if err := g.client.Call("Plugin.InstallPlugin", _args, _returns); err != nil {
-		log.Printf("RPC call to InstallPlugin API failed: %s", err.Error())
-	}
-	return _returns.A, _returns.B
-}
-
-func (s *apiRPCServer) InstallPlugin(args *Z_InstallPluginArgs, returns *Z_InstallPluginReturns) error {
-	if hook, ok := s.impl.(interface {
-		InstallPlugin(file io.Reader, replace bool) (*model.Manifest, *model.AppError)
-	}); ok {
-		returns.A, returns.B = hook.InstallPlugin(args.A, args.B)
-	} else {
-		return encodableError(fmt.Errorf("API InstallPlugin called but not implemented."))
-	}
-	return nil
-}
-
 type Z_KVSetArgs struct {
 	A string
 	B []byte