New component : Empty state (#890)

* empty_state component added

* empty_state component added

* Correction and new example

* rename status_code to header

* Enhance empty_state component documentation and template to support rich text formatting. Update docs with detailed descriptions and examples, and modify Handlebars template to conditionally render Markdown content.

* add and document class and id attributes

---------

Co-authored-by: lovasoa <contact@ophir.dev>

Author: olivierauverlot

examples/official-site/sqlpage/migrations/60_empty_state.sql

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+INSERT INTO component(name, icon, description, introduced_in_version) VALUES
+    ('empty_state', 'info-circle', 'Displays a large placeholder message to communicate a single information to the user and invite them to take action.
+
+Typically includes a title, an optional icon/image, descriptive text (rich text formatting and images supported via Markdown), and a call-to-action button.
+
+Ideal for first-use screens, empty data sets, "no results" pages, or error messages.', '0.35.0');
+
+INSERT INTO parameter(component, name, description, type, top_level, optional) SELECT 'empty_state', * FROM (VALUES
+    ('title','Description of the empty state.','TEXT',TRUE,FALSE),
+    ('header','Text displayed on the top of the empty state.','TEXT',TRUE,TRUE),
+    ('icon','Name of an icon to be displayed on the top of the empty state.','ICON',TRUE,TRUE),
+    ('image','The URL (absolute or relative) of an image to display at the top of the empty state.','URL',TRUE,TRUE),
+    ('description','A short text displayed below the title.','TEXT',TRUE,TRUE),
+    ('link_text','The text displayed on the button.','TEXT',TRUE,FALSE),
+    ('link_icon','Name of an icon to be displayed on the left side of the button.','ICON',TRUE,FALSE),
+    ('link','The URL to which the button should navigate when clicked.','URL',TRUE,FALSE),
+    ('class','Class attribute added to the container in HTML. It can be used to apply custom styling to this item through css.','TEXT',TRUE,TRUE),
+    ('id','ID attribute added to the container in HTML. It can be used to target this item through css or for scrolling to this item through links (use "#id" in link url).','TEXT',TRUE,TRUE)
+) x;
+
+INSERT INTO example(component, description, properties) VALUES
+    ('empty_state', '
+This example shows how to create a 404-style "Not Found" empty state with 
+ - a prominent header displaying "404",
+ - a helpful description suggesting to adjust search parameters, and
+ - a "Search again" button with a search icon that links back to the search page.
+',
+    json('[{
+        "component": "empty_state",
+        "title": "No results found",
+        "header": "404",
+        "description": "Try adjusting your search or filter to find what you''re looking for.",
+        "link_text": "Search again",
+        "link_icon": "search",
+        "link": "#not-found",
+        "id": "not-found"
+    }]')),
+    ('empty_state', '
+It''s possible to use an icon or an image to illustrate the problem.
+',
+    json('[{
+        "component": "empty_state",
+        "title": "A critical problem has occurred",
+        "icon": "mood-wrrr",
+        "description_md": "SQLPage can do a lot of things, but this is not one of them.
+
+Please restart your browser and **cross your fingers**.",
+        "link_text": "Close and restart",
+        "link_icon": "rotate-clockwise",
+        "link": "#"
+    }]'));
+

sqlpage/templates/empty_state.handlebars

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+<div class="empty{{#if class}} {{class}}{{/if}}"{{#if id}} id="{{id}}"{{/if}}>
+  {{#if header}}
+    <div class="empty-header">{{header}}</div>
+  {{else}}
+    {{#if icon}}
+      <div class="empty-icon">
+        <span>{{icon_img icon }}</span>
+      </div>
+    {{else}}
+      {{#if image}}
+        <div class="empty-img"><img src="{{image}}" height="128" alt="{{image}}"/></div>
+      {{/if}}
+    {{/if}}
+  {{/if}}
+  <p class="empty-title">{{title}}</p>
+  <div class="empty-subtitle text-secondary remove-bottom-margin">
+    {{~#if description}}<p>{{description}}</p>{{/if~}}
+    {{~#if description_md~}}
+      {{{markdown description_md}}}
+    {{~/if~}}
+  </div>
+
+  <div class="empty-action">
+    <a href="{{link}}" class="btn btn-primary">
+      <span class="me-1">{{icon_img link_icon}}</span>
+      {{link_text}}
+    </a>
+  </div>
+</div>