ci(docs): Fail when build aborts from broken links (#2266)

Using `set -ex` will exit the script as soon as a non-zero exit code is returned, such as when the docker image fails building the docs due to `build --strict` catching broken links. This also removes the need for `|| exit` when changing directory.

This seems fine for a small script, but AFAIK an alternative fix is just adding `|| exit` to the end of the `docker run` command too? There appears to be advice [against adopting `-e` carelessly](http://mywiki.wooledge.org/BashFAQ/105), while others [encourage `-e`](http://redsymbol.net/articles/unofficial-bash-strict-mode/). I know that several maintainers here have preference towards `set -e` so I've kept the original PR solution.

Additionally:

- `-x` is used to improve command visibility when reviewing the workflow log output.
- `--name` isn't necessary, but was part of the original PR.
- I've chosen not to include `-o pipefail`, only because no pipes are used in this script.

* docs(fix): Fix broken links

* ci(docs): Added inline docs

Extra documentation context for maintainers to quickly grok what's going on.

* chore(docs): Minor typo fix by wernerfred

Added from their related PR by request.

docs/content/examples/tutorials/basic-installation.md

@@ -144,8 +144,8 @@ In this setup `docker-mailserver` is not intended to receive email externally, s
 [docs-ports]: ../../config/security/understanding-the-ports.md
 [docs-setup-script]: ../../config/setup.sh.md
 [docs-environment]: ../../config/environment.md
-[docs-spf]: ../../config/best-practice/spf.md
-[docs-dkim]: ../../config/best-practice/dkim.md
+[docs-spf]: ../../config/best-practices/spf.md
+[docs-dkim]: ../../config/best-practices/dkim.md
 [docs-ssl]: ../../config/security/ssl.md#lets-encrypt-recommended
 
 [github-issue-1405-comment]: https://github.com/docker-mailserver/docker-mailserver/issues/1405#issuecomment-590106498