templates: add django blocks around login/registration templates (#38262)

src/authentic2/templates/authentic2/login_password_registration_form.html

@@ -1,7 +1,9 @@
 {% load i18n %}
 
+{% block registration %}
 <form enctype="multipart/form-data" method="post">
   {% csrf_token %}
   {{ form.as_p }}
   <button class="submit-button">{% trans 'Submit' %}</button>
 </form>
+{% endblock %}

src/authentic2_auth_fc/templates/authentic2_auth_fc/login.html

@@ -1,6 +1,7 @@
 {% load staticfiles %}
 {% load i18n %}
 
+{% block login %}
 <link rel="stylesheet" type="text/css" href="{% static 'authentic2_auth_fc/css/fc.css' %}">
 <div id="fc-button-wrapper">
   <div id="fc-button">
@@ -14,3 +15,4 @@
 </div>
 {% include "authentic2_auth_fc/explanation.html" %}
 {% if popup %}<script src="{% static 'authentic2_auth_fc/js/fc.js' %}" type="text/javascript"></script>{% endif %}
+{% endblock %}

src/authentic2_auth_fc/templates/authentic2_auth_fc/registration.html

@@ -1,6 +1,7 @@
 {% load staticfiles %}
 {% load i18n %}
 
+{% block registration %}
 <link rel="stylesheet" type="text/css" href="{% static 'authentic2_auth_fc/css/fc.css' %}"/>
 <div id="fc-button-wrapper">
   <div id="fc-button">
@@ -14,3 +15,4 @@
 </div>
 {% include "authentic2_auth_fc/explanation.html" %}
 {% if popup %}<script src="{% static 'authentic2_auth_fc/js/fc.js' %}" type="text/javascript"></script>{% endif %}
+{% endblock %}

src/authentic2_auth_oidc/templates/authentic2_auth_oidc/login.html

@@ -1,4 +1,6 @@
+{% block login %}
 <p id="oidc-p-{% firstof provider.slug provider.name|slugify %}">
   <a id="oidc-a-{% firstof provider.slug  provider.name|slugify %}"
      href="{{ login_url }}">{{ provider.name }}</a>
 </p>
+{% endblock %}

src/authentic2_auth_saml/templates/authentic2_auth_saml/login.html

@@ -1,7 +1,10 @@
-{% load i18n %}<form method="post">
+{% load i18n %}
+
+{% block login %}
+<form method="post">
     <button class="submit-button" name="{{ submit_name }}">{% trans "Login" %}</button>
     {% if cancel %}
         <button class="cancel-button" name="cancel" formnovalidate>{% trans 'Cancel' %}</button>
     {% endif %}
 </form>
-
+{% endblock %}