Add MPT Metadata Schema section to concept docs

- Updates MPT Concept docs with metadata schema
- Updates issue-mpt-with-metdata example code with new schema changes.

_code-samples/issue-mpt-with-metadata/js/issue-mpt-with-metadata.js

@@ -10,26 +10,26 @@ const { wallet } = await client.fundWallet()
 
 // Define metadata as JSON
 const mpt_metadata = {
-  ticker: 'TBILL',
-  name: 'T-Bill Yield Token',
-  desc: 'A yield-bearing stablecoin backed by short-term U.S. Treasuries and money market instruments.',
-  icon: 'https://example.org/tbill-icon.png',
-  asset_class: 'rwa',
-  asset_subclass: 'treasury',
-  issuer_name: 'Example Yield Co.',
-  urls: [
+  t: 'TBILL',
+  n: 'T-Bill Yield Token',
+  d: 'A yield-bearing stablecoin backed by short-term U.S. Treasuries and money market instruments.',
+  i: 'https://example.org/tbill-icon.png',
+  ac: 'rwa',
+  as: 'treasury',
+  in: 'Example Yield Co.',
+  us: [
     {
-      url: 'https://exampleyield.co/tbill',
-      type: 'website',
-      title: 'Product Page'
+      u: 'https://exampleyield.co/tbill',
+      c: 'website',
+      t: 'Product Page'
     },
     {
-      url: 'https://exampleyield.co/docs',
-      type: 'docs',
-      title: 'Yield Token Docs'
+      u: 'https://exampleyield.co/docs',
+      c: 'docs',
+      t: 'Yield Token Docs'
     }
   ],
-  additional_info: {
+  ai: {
     interest_rate: '5.00%',
     interest_type: 'variable',
     yield_source: 'U.S. Treasury Bills',