BAU: Fix content to refer to go-live page

Previously this content referred to the join public beta page,
which was removed in a previous PR[1]. However this small bit of
content was forgotten. This updates the phrasing and link to refer
to the new page 'Go live with GOV.UK One Login'

[1]- #872

express/src/views/clients/client-details.njk

@@ -434,7 +434,7 @@
   <hr class="govuk-section-break govuk-section-break--s govuk-section-break--visible govuk-!-margin-bottom-7 govuk-!-margin-top-7">
 
   <h2 class="govuk-heading-m govuk-!-margin-bottom-2">Production client</h2>
-  <p class="govuk-body govuk-!-margin-top-3">You can add a production client if you <a class="govuk-link" href="/services/{{ serviceId }}/clients/{{ clientId }}/{{ selfServiceClientId }}/public-beta">join our public beta</a>.</p>
+  <p class="govuk-body govuk-!-margin-top-3">You can add a production client if you <a class="govuk-link" href="/services/{{ serviceId }}/clients/{{ clientId }}/{{ selfServiceClientId }}/go-live">go live with GOV.UK One Login</a>.</p>
 {% endblock %}
 
 {% block scripts %}