[pulsar-function-go]add secrets provider for golang function

Is your enhancement request related to a problem? Please describe. currently go function do not have secrets provider implemented. for Java and Python functions, we already have secrets providers implemented, such as EnvironmentBasedSecretsProvider and ClearTextSecretsProvider.

this enhancement is also mentioned in https://github.com/apache/pulsar/pull/8352 and https://github.com/apache/pulsar/pull/8365

as @sijie request, this issue is used to track down the develop progress of golang function's secrets providers, and will linked with k8s golang runtime's KubernetesSecretsProviderConfigurator