File/Directory watches not set for Generic Secrets via SDS

[ruwaifaa]

Title: GenericSecrets stored in separate files do not have inotify watches

Description:
Unlike for TLS certificates, envoy does not set inotify watches if the secrets are stored using filename as a datasource option

In the example config below, envoy won't set inotify watch on secret.txt so any changes in that file won't be picked up automatically

envoy.yaml

  credentials:
    token_secret:
      name: token
      sds_config:
        path_config_source: 
          path: "/Users/ruwaifaa/token.yaml"

token.yaml

resources:
  - "@type": "type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.Secret"
    name: token
    generic_secret:
      secret:
        filename: secret.txt

This happens because SDS API returns an empty vector for datasource filenames for generic secrets here

Inotify is set for the config file however, so any changes to inline_secret or inline_bytes get propagated properly. The issue only lies when filename option is used

Is someone working on it currently? I figure this would useful for existing oauth2 filter and also when developing custom filters involving generic secrets

[optional Relevant Links:]

Any extra documentation required to understand the issue.

[phlax]

Is someone working on it currently?

not that im aware of

cc @ggreenway

[phlax]

possibly related #19582

cc @LuyaoZhong

[ggreenway]

Is someone working on it currently?

not that im aware of

cc @ggreenway

SDS isn't my area of expertise

[phlax]

SDS isn't my area of expertise

apologies i was struggling to find a codeowner and thought you may have some expertise in this area

cc @adisuissa (who may know more)

[LuyaoZhong]

possibly related #19582

cc @LuyaoZhong

This is not related to #19582, it should be developed as a separate feature.

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[github-actions]

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