hide left sidebar and switch to links

[oadetayo]

Pull request overview

This PR replaces the use of shiny::tabPanel() with a hidden bslib::navset_hidden sidebar. The navigation is now handled via links

What is the current behaviour?

Previously, the app used a sidebar for navigation

What is the new behaviour?

The app now uses bslib::navset_hidden, which allows for a hidden sidebar navigation.
Users access different views via links instead of visible tab panels.

[cjrace]

Suggested change to how the dfe_contents function works, and a couple of other things:

1. Can you update the units package in the lockfile - think it should be 0.8-7 now as they release a bug fix really quickly after the 0.8-6 release

2. Can we add a bit more space / padding on the left of the contents so it's not as close to the side of the screen?

3. Can we reduce the whitespace between the h1 on each page and the header - it's grown a bit with the move to the left navigation and it's too much now

[cjrace]

Thanks @oadetayo! Happy those comments are resolved now, still some funky things going on style-wise, though happy for those to be picked up separately as I don't think they were introduced by this PR (same with the test failures)

Branch is almost ready to go in, though when updating and testing I noticed a couple of things still to address:

1. Whitespace bar in the footer
2. Bar of whitespace above header after cookies are accepted
3. Whitespace above content is still a bit much (least important / can cope without changing)

[rmbielby]

Couple of small things:

1. We don't really need the accessibility, cookies and support panels linking from the sidebar as they're all linked from the footer already
2. Those three above have a different page margin going on to the Example tab and user guide
3. Bonus one, there is only one example tab, so could just remove the 1...

[cjrace]

Done your changes above @rmbielby - now also fixing the footer links and adding backlinks in in line with the latest development version of shinyGovstyle, will push my changes up later

[rmbielby]

Abandoning this one as superseded by recent newer developments in shinyGovstyle.