Add gofmt check in workflows

[Xuanwo]

We need to add gofmt check to make sure every PR has been formatted.

Like https://github.com/digitalocean/godo/pull/396/files

We should add the following action .github/workflows/gofmt.yml in every golang related repos:

name: "gofmt"

on: [ push,pull_request ]

jobs:
  gofmt:
    name: gofmt
    runs-on: ubuntu-latest

    steps:
      - name: Set up Go 1.x
        uses: actions/setup-go@v2
        with:
          go-version: "1.15"

      - name: Checkout repository
        uses: actions/checkout@v2

      - name: Format
        run: if [ "$(gofmt -l . | wc -l)" -gt 0 ]; then exit 1; fi

Tips:

• Should be make build, as make build will format all code.

Todo Lists

• fix: added gofmt to action #660
• Add gofmt check in unittest go-service-ipfs#8
• feat: add gofmt action in go-coreutils go-coreutils#9
• ci: add gofmt action go-service-azblob#33
• add gofmt action for go-service-cos go-service-cos#37
• add gofmt action for go-service-dropbox go-service-dropbox#26
• add gofmt action for go-service-fs go-service-fs#50
• add gofmt action for go-service-gcs go-service-gcs#41
• add gofmt action for go-service-kodo go-service-kodo#34
• add gofmt action for go-service-oss go-service-oss#35
• add gofmt action for go-service-qingstor go-service-qingstor#62
• add gofmt action for go-service-s3 go-service-s3#140
• ci: Add gofmt action go-service-uss#14
• add gofmt action for go-service-example go-service-example#8

[burntcarrot]

@Xuanwo I have created a PR. Requesting review.