[Backport] Version bumps from 1.6.0 release (#2965)

This PR backports version bumps from release branch
`release-polkadot-v1.6.0` back to `master` and also moved `prdoc` files
related to the release to the appropriate folder

prdoc/1.6.0/pr_1694.prdoc

@@ -0,0 +1,24 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Agile Coretime Base Relaychain Functionality
+
+doc:
+  - audience: Runtime User
+    description: |
+      The relay chain is now capable of receiving assignments from the coretime
+      chain and will schedule parachains and on-demand orders accordingly.
+      Existing leases and system chains are preserved. They get a reserved
+      coretime core via a migration. 
+migrations: 
+  db: []
+  runtime: 
+    - reference: polkadot-runtime-parachains
+      description: |
+        Claim queue in scheduler now no longer contains Option values and
+        assignments now contain information necessary to accomodate for coretime
+        features. Also all existing parachains are converted to coretime
+        assignments.
+
+crates:
+  - name: polkadot-runtime-parachains