[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_1343.prdoc

@@ -0,0 +1,29 @@
+title: Tasks API - A general system for recognizing and executing service work
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      The Tasks API allows you to define some service work that can be recognized by a script or an off-chain worker.
+      Such a script can then create and submit all such work items at any given time.
+      `#[pallet:tasks_experimental]` provides a convenient way to define such work items. It can be attached to an 
+      `impl` block inside a pallet, whose functions can then be annotated by the following attributes:
+      1. `#[pallet::task_list]`: Define an iterator over the available work items for a task
+      2. `#[pallet::task_condition]`: Define the conditions for a given work item to be valid
+      3. `#[pallet::task_weight]`: Define the weight of a given work item
+      4. `#[pallet::task_index]`: Define the index of a given work item
+      Each such function becomes a variant of the autogenerated enum `Task<T>` for this pallet. 
+      All such enums are aggregated into a `RuntimeTask` by `construct_runtime`.
+      An example pallet that uses the Tasks API is available at `substrate/frame/example/tasks`.
+
+migrations:
+  db: []
+
+  runtime: []
+
+crates:
+  - name: frame-system
+  - name: frame-support
+  - name: frame-support-procedural
+  - name: pallet-example-tasks
+
+host_functions: []