update operator-sdk to v0.19.0

- Update `github.com/operator-framework/operator-sdk` dependency to [v0.19.0](https://github.com/operator-framework/operator-sdk/tree/v0.19.0) which is the latest available and has the [following changes](https://github.com/operator-framework/operator-sdk/releases/tag/v0.19.0)

.circleci/config.yml

@@ -7,7 +7,7 @@ executors:
   default:
     working_directory: /go/src/github.com/mattermost/mattermost-operator
     docker:
-      - image: circleci/golang:1.14.4
+      - image: circleci/golang:1.14.6
 
 jobs:
   lint:
@@ -57,7 +57,7 @@ jobs:
       - IMAGE_NAME=mattermost/mattermost-operator
       - IMAGE_TAG=test
       - KIND_VERSION=v0.8.1
-      - SDK_VERSION=v0.18.2
+      - SDK_VERSION=v0.19.0
     machine: true
     resource_class: 2xlarge
     working_directory: /home/circleci/.go_workspace/src/github.com/mattermost/mattermost-operator

Makefile

@@ -1,9 +1,9 @@
 .PHONY: all check-style unittest generate build clean build-image operator-sdk yaml
 
 OPERATOR_IMAGE ?= mattermost/mattermost-operator:test
-SDK_VERSION = v0.18.2
+SDK_VERSION = v0.19.0
 MACHINE = $(shell uname -m)
-BUILD_IMAGE = golang:1.14.4
+BUILD_IMAGE = golang:1.14.6
 BASE_IMAGE = alpine:3.12
 GOROOT ?= $(shell go env GOROOT)
 GOPATH ?= $(shell go env GOPATH)