Remove Hashicorp Vault from Secret Store example

[artursouza]

Describe the proposal

There was a change in Hashicorp Vault output that broke the example validation. Instead, use the local file secret store so there is no need to install Hashicorp Vault anymore.

This work needs to make sure the instructions in the README.md file for the example is reworded to explain how the secret is retrieved. In addition, it should point to the documentation in Dapr docs website where other secret store components can be used.

Change should also remove Vault installation from the validate.yaml workflow file.

[fackee]

/assign