chore: switch default branch to 10.x (#789)

Switch the default branch to 10.x, while making 3.x a release
branch.

Related #784

.projenrc.js

@@ -6,10 +6,11 @@ const project = new cdk.JsiiProject({
   repository: 'https://github.com/aws/constructs.git',
 
   // release branches
-  defaultReleaseBranch: 'main',
-  majorVersion: 3,
+  defaultReleaseBranch: '10.x',
+  majorVersion: 10,
+  npmDistTag: 'latest',
   releaseBranches: {
-    '10.x': { majorVersion: 10 },
+    '3.x': { majorVersion: 3, npmDistTag: 'latest-3' },
   },
 
   // author
@@ -58,11 +59,6 @@ const project = new cdk.JsiiProject({
 
   compat: true,
 
-  //----------------------------------------------------
-  // pre-release 10.x: publish "next" dist-tag and do not publish non-npm languages
-  //----------------------------------------------------------
-  npmDistTag: 'next',
-
   projenUpgradeSecret: 'PROJEN_GITHUB_TOKEN',
   autoApproveOptions: {
     allowedUsernames: ['aws-cdk-automation'],