Plugins: Use grafana-plugin-sdk-go v0.5.0 (#21116)

* fix dispense

* plugin loading refactor

Moves common functionality of registering, starting,
stopping and restarting backend plugins to
backendplugin package.

* simplify plugin descriptors

* target sdk v0.5.0

Co-authored-by: Kyle Brandt <kyle@kbrandt.com>

vendor/github.com/json-iterator/go/any_bool.go

@@ -0,0 +1,137 @@
+package jsoniter
+
+type trueAny struct {
+	baseAny
+}
+
+func (any *trueAny) LastError() error {
+	return nil
+}
+
+func (any *trueAny) ToBool() bool {
+	return true
+}
+
+func (any *trueAny) ToInt() int {
+	return 1
+}
+
+func (any *trueAny) ToInt32() int32 {
+	return 1
+}
+
+func (any *trueAny) ToInt64() int64 {
+	return 1
+}
+
+func (any *trueAny) ToUint() uint {
+	return 1
+}
+
+func (any *trueAny) ToUint32() uint32 {
+	return 1
+}
+
+func (any *trueAny) ToUint64() uint64 {
+	return 1
+}
+
+func (any *trueAny) ToFloat32() float32 {
+	return 1
+}
+
+func (any *trueAny) ToFloat64() float64 {
+	return 1
+}
+
+func (any *trueAny) ToString() string {
+	return "true"
+}
+
+func (any *trueAny) WriteTo(stream *Stream) {
+	stream.WriteTrue()
+}
+
+func (any *trueAny) Parse() *Iterator {
+	return nil
+}
+
+func (any *trueAny) GetInterface() interface{} {
+	return true
+}
+
+func (any *trueAny) ValueType() ValueType {
+	return BoolValue
+}
+
+func (any *trueAny) MustBeValid() Any {
+	return any
+}
+
+type falseAny struct {
+	baseAny
+}
+
+func (any *falseAny) LastError() error {
+	return nil
+}
+
+func (any *falseAny) ToBool() bool {
+	return false
+}
+
+func (any *falseAny) ToInt() int {
+	return 0
+}
+
+func (any *falseAny) ToInt32() int32 {
+	return 0
+}
+
+func (any *falseAny) ToInt64() int64 {
+	return 0
+}
+
+func (any *falseAny) ToUint() uint {
+	return 0
+}
+
+func (any *falseAny) ToUint32() uint32 {
+	return 0
+}
+
+func (any *falseAny) ToUint64() uint64 {
+	return 0
+}
+
+func (any *falseAny) ToFloat32() float32 {
+	return 0
+}
+
+func (any *falseAny) ToFloat64() float64 {
+	return 0
+}
+
+func (any *falseAny) ToString() string {
+	return "false"
+}
+
+func (any *falseAny) WriteTo(stream *Stream) {
+	stream.WriteFalse()
+}
+
+func (any *falseAny) Parse() *Iterator {
+	return nil
+}
+
+func (any *falseAny) GetInterface() interface{} {
+	return false
+}
+
+func (any *falseAny) ValueType() ValueType {
+	return BoolValue
+}
+
+func (any *falseAny) MustBeValid() Any {
+	return any
+}