SEC-281: Add awareness of HSTS to secutiry.adoc for strict transport security.

[kemister85]

Ticket: SEC-281

Site: Staging branch

Changes:

• Include recommendation for HSTS to security.adoc.

Pre-checks:

• Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/.

Review:

• Documentation Team Lead has reviewed

[FarzadHayat]

Nice work. Just some thoughts on the location of the section. I think this doesn't really belong in the "What we do to maintain security for TinyMCE" section since it's more of a recommendation for our integrators rather than anything that we are doing in the TinyMCE editor. My opinion is that this should be a level 2 heading (instead of level 3 heading) and located after the "What we do to maintain security for TinyMCE" section and before the "Configuring Content Security Policy (CSP) for TinyMCE" section,

...
To protect our users, {companyname} ensures that the TinyMCE dependencies are updated before the next version (major or minor) is released.

[[enforcing-https-with-hsts]]
== Enforcing HTTPS with HSTS

...

include::partial$misc/general-csp.adoc[]
...

add a link to the section in the Overview

...
** xref:keeping-dependencies-up-to-date[Keeping dependencies up-to-date]
* xref:enforcing-https-with-hsts[Enforcing HTTPS with HSTS]
* xref:configuring-content-security-policy-csp-for-tinymce[Configuring Content Security Policy (CSP) for TinyMCE]
...

and add a list item to the "What we do to maintain security for TinyMCE" section with content something like: "Provides information about how to configure enforcing HTTPS with HSTS."

...
* Keeps {productname} dependencies up to date, and
* Provides information about how to configure enforcing HTTPS with HSTS, and
* Provides information about how to configure a Content Security Policy that works with {productname}.

Hope that makes sense. I can't put in a suggestions because the other sections of the file are not part of the PR file diff.

[WayneWWong]

@kemister85
Good morning Karl, many thanks for progressing this task. I reviewed the change, I do not have comments and I approve the content.
Many thanks and kind regards,
Wayne