Setup examples with mechanical-markdown

## Describe the proposal

Use https://github.com/dapr/mechanical-markdown to update the examples folder. Also add a CI pipeline to validate if all the examples run successfully. This will ensure that our examples are always up to date.

For reference, see https://github.com/dapr/java-sdk/

1. CI pipeline - https://github.com/dapr/java-sdk/blob/master/.github/workflows/validate.yml
2. Sample example - https://raw.githubusercontent.com/dapr/java-sdk/master/examples/src/main/java/io/dapr/examples/pubsub/http/README.md