mergify and contributing guidelines

.github/mergify.yml

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+defaults:
+  actions:
+    backport:
+      assignees:
+        - "{{ author }}"
+
+queue_rules:
+  - name: default
+    conditions:
+      - "#approved-reviews-by>=1"
+
+pull_request_rules:
+  - name: automerge to the base branch with label automerge and branch protection passing
+    conditions:
+      - "#approved-reviews-by>=1"
+      - base=main
+      - label=A:automerge
+    actions:
+      queue:
+        name: default
+        method: squash
+        commit_message_template: |
+          {{ title }} (#{{ number }})
+          {{ body }}
+  - name: backport patches to osmosis-main branch
+    conditions:
+      - base=main
+      - label=A:backport/osmosis-main
+    actions:
+      backport:
+        branches:
+          - osmosis-main
+  - name: backport patches to v22.x branch
+    conditions:
+      - base=main
+      - label=A:backport/v22.x
+    actions:
+      backport:
+        branches:
+          - v22.x
+  - name: backport patches to v23.x branch
+    conditions:
+      - base=main
+      - label=A:backport/v23.x
+    actions:
+      backport:
+        branches:
+          - v23.x

CONTRIBUTING.md

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+# Contributing Guidelines
+
+## Branch Management
+
+While in [osmosis](https://github.com/osmosis-labs/osmosis), we develop against a `main` branch and then backport to release branches such as [v21.x](https://github.com/osmosis-labs/osmosis/tree/v21.x).
+
+Each release branch and the main branch might rely on incompatible dependencies.
+Therefore, we must maintain parity between SQS and Osmosis branches.
+
+While in `osmosis`, `main` is the default working branch, this is not the case in `sqs`.
+
+Here, we always develop on the currently live major branch (e.g. `v21.x`) by default but keep backporting with [labels](https://github.com/osmosis-labs/sqs/tree/main/.github/mergify.yml) to `main` branch. 
+
+Once chain upgrades to the next major, cut a new release branch (e.g. `v22.x` ) from `main` in `sqs`,
+make `v22.x` as default and completely drop the old `v21.x` while continuing to backport to `main`.
+
+To sum up,
+- `sqs/vx.x` always references `osmosis/v.x.x`
+   * This is the default repository branch
+- `sqs/main` always references `osmosis/main`
+   * This is the branch we maintain to cut the new major branch once chain release happens
+