Rework spellchecking, add lint-spell (#29112)

Backport clean cherry-picks of
9c39f8515f
and
c7a21cbb0c
onto 1.21.

- Use maintained fork https://github.com/golangci/misspell
- Rename `mispell-check` to `lint-spell`, add `lint-spell-fix`
- Run `lint-spell` in separate actions step
- Lint more files, fix discovered issues
- Remove inaccurate and outdated info in docs (we do not need GOPATH for
tools anymore)

Maybe later we can add more spellchecking tools, but I have not found
any good ones yet.

.github/workflows/pull-compliance.yml

@@ -64,6 +64,18 @@ jobs:
       - run: make deps-frontend
       - run: make lint-swagger
 
+  lint-spell:
+    if: needs.files-changed.outputs.backend == 'true' || needs.files-changed.outputs.frontend == 'true' || needs.files-changed.outputs.actions == 'true' || needs.files-changed.outputs.docs == 'true' || needs.files-changed.outputs.templates == 'true'
+    needs: files-changed
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          check-latest: true
+      - run: make lint-spell
+
   lint-go-windows:
     if: needs.files-changed.outputs.backend == 'true' || needs.files-changed.outputs.actions == 'true'
     needs: files-changed