Replace content & config with tech-docs version

[digitalronin]

This change converts the site to use (a patched
version of) the gov.uk tech-docs template & gems.

https://github.com/alphagov/tech-docs-template

You can see what the site will look like after this PR is merged here:
https://ministryofjustice.github.io/technical-guidance2/
(that repository and site will be deleted after this PR is merged).

After merging this PR, this repository's settings will need to be changed so that github pages publishes the /docs folder of the gh-pages branch.

Details of the patch are here:
ministryofjustice/cloud-platform-user-guide#393

This gives the site a search feature, as well as
dynamic review dates (i.e. you see a big red
banner at the foot of the page if the content was
not reviewed when it should have been).

Publishing is now done via a github action. See:

.github/workflows/publish.yml

...for details.

[SteveMarshall]

This is great, but it'd be nice if it was possible to have the homepage dynamically generated again. Or does that page become irrelevant under the new system?

[SteveMarshall]

Is it possible to maintain the dynamic generation of this page?

[digitalronin]

I'm not sure, TBH. tech-docs is based on middleman rather than jekyll, but I imagine middleman has the same kind of features for doing that. I'll look into it.

[digitalronin]

does that page become irrelevant under the new system?

No, it's still important. We just maintain the index page manually for our user-guide site. The nice thing about that is that you can prepare a page in advance and not necessarily index it until later.

e.g. this page for our CLI

https://user-guide.cloud-platform.service.justice.gov.uk/documentation/getting-started/cloud-platform-cli.html#the-cloud-platform-cli

It was quite useful to have that in place and not indexed at first, while we were working on things. But I will have a look and see how we could do the same thing with middleman. I'm sure it must be possible.