Add `slither.config.json` to the template instead of hardcoding config params in the CI.

For more flexibility and being able to run slither with the same params locally and in CI.

Remove from CI:
```
slither-args: --filter-paths "./lib|./test" --exclude naming-convention,solc-version
```
Add `slither.config.json` to the template:
```
{
  "detectors_to_exclude": "naming-convention,solc-version",
  "filter_paths": "(./lib|./test)"
}
```