* FT ignore versions via env variable DEPENDABOT_IGNORED_VERSIONS

Environment variable format is following:

```json
{
  "vendor/packageA": [
    ">0.1.0",
    "<1.0.0"
  ],
  "vendor/packageB": [
    "^2.0.0"
  ]
}
```

By default there are no ignored versions

* SR include documentation

Co-authored-by: Oleksandr Vasylenko <oleksandr.vasylenko@flixbus.com>