Feat: Add shared danger file to ipfs repos

[SgtPooki]

Context: In awesome-ipfs, I added https://github.com/ipfs/awesome-ipfs/blob/master/dangerfile.js which can help to block and give more information in a comment on PRs. I talked with @lidel about this and we agreed that this would be a good addition to many of our repos.

Danger currently only has official runners for JS, ruby, swift, python, and kotlin, but there is the possibility to create a danger-runner in any language (Go, Rust, etc..): https://danger.systems/js/usage/danger-process.html
The ask for this issue is that we come up with a base file that would work for multiple repos to use as a default. Some default rules we could use are:

1. Warning on large PRs (over X lines changed)
2. Fail when src/ is modified without test/ modified
3. Display lint/test failures
4. Display code coverage changes (This should probably be done via codecov)

And there are other examples and plugins listed at https://danger.systems/js/

---

A few issues I could see with implementing this in github-mgmt:

1. Accidentally overwriting a customized danger file
2. Setting rules that are too strict for some repos

So I guess the main goal here is to make it easy for ipfs repos to get a danger file that works, and then be allowed to modify it for their needs as appropriate.

[SgtPooki]

There is a large example with some fairly useful stuff at https://github.com/apollographql/apollo-client/blob/6d49d993c6cf0eb0fcf04b0a718a8be2ada3c542/config/dangerfile.ts, though they have since removed it from their repo

[SgtPooki]

example improvement that could be made to ipfs/awesome-ipfs to give helpful hints in PRs:

const { danger, markdown, fail, warn, message } = require('danger')

danger.git.modified_files.forEach(file => {
  danger.git.diffForFile(file).then(diff => {
    if (diff == null) {
      return
    }

    if (file.includes('data/')) {
      let hasTitle = false
      let hasDescription = false
      let hasImage = false
      let hasSource = false
      const entries = []
      diff.added.split('\n').forEach(line => {
        if (line.includes('picture:')) {
          hasImage = true
          // check that the image exists
          const picturePath = line.split('picture:')[1].trim()
          if (!fs.existsSync(`src/static/images/${picturePath}`)) {
            fail(`The image ${picturePath} does not exist`)
          }
        } else if (line.includes('title:')) {
          hasTitle = true
        } else if (line.includes('description:')) {
          hasDescription = true
        } else if (line.includes('source:')) {
          hasSource = true
        }
      })
      /**
       * Ensure that entries to data/ contain a
       *  1. title
       *  2. source
       *  3. description
       */
      if (!diff.added.includes('title:')) {
        fail(`Please add a title to ${file}`)
      }
      if (!diff.added.includes('source:')) {
        fail(`Please add a source to ${file}`)
      }
      if (!diff.added.includes('description:')) {
        fail(`Please add a description to ${file}`)
      }
      /**
       * Ensure that http links use https
       */
      if (diff.added.includes('http://')) {
        fail(`Please use https:// instead of http:// in ${file}`)
      }
    }
  })
})