feat(core): Add support for building LLM applications (#7235)

This extracts all core and editor changes from #7246 and #7137, so that
we can get these changes merged first.

ADO-1120

[DB Tests](https://github.com/n8n-io/n8n/actions/runs/6379749011)
[E2E Tests](https://github.com/n8n-io/n8n/actions/runs/6379751480)
[Workflow Tests](https://github.com/n8n-io/n8n/actions/runs/6379752828)

---------

Co-authored-by: Jan Oberhauser <jan.oberhauser@gmail.com>
Co-authored-by: Oleg Ivaniv <me@olegivaniv.com>
Co-authored-by: Alex Grozav <alex@grozav.com>
Co-authored-by: कारतोफ्फेलस्क्रिप्ट™ <aditya@netroy.in>

packages/editor-ui/src/n8n-theme-variables.scss

@@ -65,6 +65,13 @@ $tag-text-color: var(--color-text-dark);
 $tag-close-background-color: var(--color-text-light);
 $tag-close-background-hover-color: var(--color-text-dark);
 
+// nodes
+$node-background-default: var(--color-background-xlight);
+$node-background-executing: var(--color-primary-tint-3);
+$node-background-executing-other: #ede9ff;
+// TODO: Define that differently
+$node-background-type-other: #ede9ff;
+
 // Node creator
 $node-creator-width: 385px;
 $node-creator-text-color: var(--color-text-dark);
@@ -109,3 +116,7 @@ $version-card-box-shadow-color: hsla(
 	var(--color-background-dark-l),
 	0.07
 );
+
+// supplemental node types
+$supplemental-node-types: ai_chain ai_document ai_embedding ai_languageModel ai_memory
+	ai_outputParser ai_tool ai_retriever ai_textSplitter ai_vectorRetriever ai_vectorStore;