PubSub Pulsar: Allow for OIDC clientSecret to be rotated when token is refreshed #4102
Description
Describe the feature
Security policy requires rotating the Pulsar OAuth2 client secret (not just the token) via a file path. The current Pulsar Go client loads this file only once at startup, breaking authentication on subsequent token refreshes. The Pulsar team will add a fix to re-read the secret file on every token refresh operation. The Dapr Pulsar component then just needs to support passing a file path for the privateKey (clientSecret) metadata so that this file can be re-read on token refresh events and then re-generated.
Currently clientSecret only supports a value but by allowing this to read from a filePath then the privateKey can be rotated and then the token subsequently regenerated.
Release Note
RELEASE NOTE: ADD