Update docs pipeline to solidity-docgen@0.6 (#3707)

(cherry picked from commit c52625018b)

docs/config.js

@@ -0,0 +1,21 @@
+const path = require('path');
+const fs = require('fs');
+
+/** @type import('solidity-docgen/dist/config').UserConfig */
+module.exports = {
+  outputDir: 'docs/modules/api/pages',
+  templates: 'docs/templates',
+  exclude: ['mocks'],
+  pageExtension: '.adoc',
+  pages: (_, file, config) => {
+    // For each contract file, find the closest README.adoc and return its location as the output page path.
+    const sourcesDir = path.resolve(config.root, config.sourcesDir);
+    let dir = path.resolve(config.root, file.absolutePath);
+    while (dir.startsWith(sourcesDir)) {
+      dir = path.dirname(dir);
+      if (fs.existsSync(path.join(dir, 'README.adoc'))) {
+        return path.relative(sourcesDir, dir) + config.pageExtension;
+      }
+    }
+  },
+};