ensure there are linkable targets to all sections of the product page

[pauldougan]

As an architect working with other government departments and delivery partners I need go be able to signpost people to the most specific guidance in our product material on the use of our platform. Typically this requires the ability to refer to specific topics in email, slack, gsuite, hangouts etc.

To make sure we can point people to our material we should ensure that there are linkable targets to all the sub headings of the product documentation so that we can link to specific sections of the docs.

The tech docs does this well.

<h2 id="standard-buildpack-responsibilities" class="anchored-heading">
<a href="#standard-buildpack-responsibilities" class="anchored-heading__icon" aria-hidden="true" tabindex="-1"></a>
Standard buildpack responsibilities</h2>

For example, we now document the platform constraints at https://www.cloud.service.gov.uk/constraints

I need to be able to link to a specific section like https://www.cloud.service.gov.uk/constraints#faas

so that we I direct users to the most specific guidance possible when explaining the topic

to: whomever@other-government-department.gov.uk
subject: GOV.UK PaaS and FaaS

The GOV.UK PaaS does not support the 'functions as a service' style of application, 
see  https://www.cloud.service.gov.uk/constraints#faas

• [ ] Add targets to the sections in a way that is compatible with the design system
• [ ] test links

[pauldougan]

this is resolved in the new version of the product pages