Add context store config options and expose context commands

This will allow plugins to have custom typed endpoints, as well as
create/remove/update contexts with the exact same results as the main
CLI (thinking of things like `docker ee login https://my-ucp-server
--context ucp-prod)`

Signed-off-by: Simon Ferquel <simon.ferquel@docker.com>

cli/context/store/storeconfig.go

@@ -25,6 +25,11 @@ type Config struct {
 	endpointTypes map[string]TypeGetter
 }
 
+// SetEndpoint set an endpoint typing information
+func (c Config) SetEndpoint(name string, getter TypeGetter) {
+	c.endpointTypes[name] = getter
+}
+
 // NewConfig creates a config object
 func NewConfig(contextType TypeGetter, endpoints ...NamedTypeGetter) Config {
 	res := Config{

cli/context/store/storeconfig_test.go

@@ -0,0 +1,31 @@
+package store
+
+import (
+	"testing"
+
+	"gotest.tools/assert"
+)
+
+type testCtx struct{}
+type testEP1 struct{}
+type testEP2 struct{}
+type testEP3 struct{}
+
+func TestConfigModification(t *testing.T) {
+	cfg := NewConfig(func() interface{} { return &testCtx{} }, EndpointTypeGetter("ep1", func() interface{} { return &testEP1{} }))
+	assert.Equal(t, &testCtx{}, cfg.contextType())
+	assert.Equal(t, &testEP1{}, cfg.endpointTypes["ep1"]())
+	cfgCopy := cfg
+
+	// modify existing endpoint
+	cfg.SetEndpoint("ep1", func() interface{} { return &testEP2{} })
+	// add endpoint
+	cfg.SetEndpoint("ep2", func() interface{} { return &testEP3{} })
+	assert.Equal(t, &testCtx{}, cfg.contextType())
+	assert.Equal(t, &testEP2{}, cfg.endpointTypes["ep1"]())
+	assert.Equal(t, &testEP3{}, cfg.endpointTypes["ep2"]())
+	// check it applied on already initialized store
+	assert.Equal(t, &testCtx{}, cfgCopy.contextType())
+	assert.Equal(t, &testEP2{}, cfgCopy.endpointTypes["ep1"]())
+	assert.Equal(t, &testEP3{}, cfgCopy.endpointTypes["ep2"]())
+}