Add shellcheck step to PR process.

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Motivation

It would be good to find errors in our bash script files before updating the main branch.

Is your feature request related to a problem? Please describe.

This is more of a prevention step to make it easier for non bash experts to contribute bash scripts to the project.

Proposed Resolution

Use something similar to this.

name: Pull request checks
on: pull_request

jobs:
  lint-bash:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v1
      - name: Run ShellCheck
        uses: azohra/[email protected]
        with:
          exclude-paths: Dockerfile, .github/CODEOWNERS, .github/ISSUE_TEMPLATE