Dynamic versioning for Polkadot SDK

* Use Git Tag to get Polkadot SDK version
* Allows us to build LTS versions without having to update Dockerfile

.github/workflows/docker.yml

@@ -35,6 +35,8 @@ jobs:
           cache-to: |
             type=gha,mode=max,scope=docker-build-${{ matrix.arch }}
           context: .
+          build-args: >-
+            ${{ startsWith(github.ref, 'refs/tags/') && format('VERSION={0}', github.ref_name) || '' }}
   package:
     needs: [build]
     runs-on: ubuntu-latest
@@ -73,3 +75,5 @@ jobs:
           cache-to: |
             type=gha,mode=max,scope=docker-package
           context: .
+          build-args: >-
+            ${{ startsWith(github.ref, 'refs/tags/') && format('VERSION={0}', github.ref_name) || '' }}

Dockerfile

@@ -13,8 +13,8 @@ RUN rustup target add wasm32-unknown-unknown
 RUN rustup component add rust-src
 
 WORKDIR /opt
-ARG VERSION=polkadot-stable2412-1
-RUN git clone https://github.com/paritytech/polkadot-sdk.git -b $VERSION --depth 1
+ARG VERSION=stable2412-1
+RUN git clone https://github.com/paritytech/polkadot-sdk.git -b polkadot-$VERSION --depth 1
 WORKDIR /opt/polkadot-sdk
 RUN cargo build --locked --release \
   --bin polkadot \