Add links to Climate Action Plan Explorer plans

[garethrees]

e.g. WhatDoTheyKnow: Aberdeen City Council → UK Climate Action Plan Explorer: Aberdeen City Council

[garethrees]

The simplest way to do this is by adding a new item in the body sidebar (as we've done for NI charities and MapIt areas.

The existing pattern for linking out to external databases is to use a tag of the form database:record_id – mapit:1234, for example. I think we should continue that pattern here.

While CAPE does have some lookup code, I don't think we want to use that here. CAPE is currently only focused on local councils, which is ~1% of the bodies on WDTK. While we could generate a link for every authority for CAPE to look up based on a WDTK body identifier, the majority of them will 404 since CAPE won't have a listing.

We already have a spreadsheet mapping WDTK bodies to CAPE records, so it should be pretty trivial to write a script to apply tags to bodies in the form cape:aberdeen-city-council, and similarly trivial to add the sidebar link:

<% if public_body.has_tag?('cape') %>
  <% public_body.get_tag_values('cape').each do |tag_value| %>
      <%= link_to _('Climate Action Plan'),
                    "https://data.climateemergency.uk/councils/#{ tag_value }" %><br>
  <% end %>
<% end %>

I'm not too concerned about the maintenance aspect here, since the generation of the WDTK/CAPE slug mapping is automatable and we're dealing with a handful of authorities that don't change too frequently.

If we want some fancier styling then I'm sure @zarino can arrange that within the confines of the sidebar.

[garethrees]

Just noting that this might be a nice issue for our new cross-programme developer to work on as a relatively easy intro to both CAPE and Alaveteli/WDTK, and includes a bit of data munging (script to add/update tags) + a bit of UI.