Run codespell on CI

This commit introduces a codespell config skipping over non-code files
and a CI job running codespell using the config.
Issue: payjoin#561

Author: arminsabouri

.codespellrc

@@ -0,0 +1,3 @@
+[codespell]
+skip = .git,target,Cargo.toml,Cargo.lock,Cargo-minimal.lock,Cargo-recent.lock
+ignore-words-list = crate,ser

.github/workflows/rust.yml

@@ -73,3 +73,10 @@ jobs:
         run: bash contrib/coverage.sh
       - name: "Upload report to coveralls"
         uses: coverallsapp/github-action@v2
+  
+  CodeSpell: 
+    name: Code spell check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: codespell-project/actions-codespell@v2