chore: consolidate two expensive blocks table migrations (#2136)

Author: zone117x

migrations/1729262745699_stacks_block_signer-signatures.js renamed to migrations/1729520843350_stacks_block_tenure-height-signer-signatures.js

@@ -3,6 +3,12 @@
 /** @param { import("node-pg-migrate").MigrationBuilder } pgm */
 exports.up = pgm => {
 
+  pgm.addColumn('blocks', {
+    tenure_height: {
+      type: 'integer',
+    }
+  });
+
   pgm.addColumn('blocks', {
     signer_signatures: {
       type: 'bytea[]',