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/config/user-management/accounts.md

@@ -41,7 +41,7 @@ You will then be asked for a password, and be given back the data for a new acco
 
 - `imap-quota` is enabled and allow clients to query their mailbox usage.
 - When the mailbox is deleted, the quota directive is deleted as well.
-- Dovecot quotas support LDAP, **but it's not implemented** (_PR are welcome!_).
+- Dovecot quotas support LDAP, **but it's not implemented** (_PRs are welcome!_).
 
 [docs-setupsh]: ../setup.sh.md
 [github-issue-552]: https://github.com/docker-mailserver/docker-mailserver/issues/552