docs: fix broken links

* Set the `NVD_API_KEY` variable with your NVD API key. :warning: This is a sensitive value, so we recommend you add it as a **masked** Gitlab variable

* Add `-DnvdApiKey=$NVD_API_KEY` to `MAVEN_DEPENDENCY_CHECK_ARGS`

In case your Gitlab runners cannot contact the NVD API (e.g. if they are not allowed to connect to the Internet), you can maintain a local data feed cache with the [vulnz](https://github.com/jeremylong/Open-Vulnerability-Project/tree/main/vulnz) tool.

In case your Gitlab runners cannot contact the NVD API (e.g. if they are not allowed to connect to the Internet), you can maintain a local data feed cache with the [vulnz](https://github.com/jeremylong/open-vulnerability-cli) tool.

In order to configure Dependency-Check to fetch the vulnerabilities from your cache you need to:

* Run the [vulnz](https://github.com/jeremylong/Open-Vulnerability-Project/tree/main/vulnz) tool in order to fetch the vulnerabilities and store them as data feeds (the data feeds will be stored as JSON files with the NVD Vulnerability Data API version 2.0 schema)

* Run the [vulnz](https://github.com/jeremylong/open-vulnerability-cli) tool in order to fetch the vulnerabilities and store them as data feeds (the data feeds will be stored as JSON files with the NVD Vulnerability Data API version 2.0 schema)

* Make these data feeds accessible via a URL reachable by your Gitlab runners

* Add `-DnvdDatafeedUrl=https://URL-OF-LOCAL-CACHE` to `MAVEN_DEPENDENCY_CHECK_ARGS`