Parameter Manager: Add Support for Remote Configuration Using the GCP Parameter Manager

[suvidha-malaviya]

Description
I would like to request a feature to the Spring Cloud GCP library, adding support for the paramconfig module. This enhancement enables the library to fetch configuration parameters stored in the GCP Parameter Manager.

Google Cloud Platform has recently introduced Parameter Manager which enables user to store the configuration in JSON, YAML and Unstructured format. I would like to add the support for fetch the configuration from remote state (GCP Parameter Manager). Both global and regional parameters would be supported.

Implementing support for paramconfig module, which will be able to fetch the JSON, YAML (flatten structure) configuration from the GCP Parameter Manager when application starts.

Proposed Changes:

• Add the support of paramconfig module in the spring-cloud-gcp-autoconfigure module which enables end user to fetch configuration stored in Parameter Manager.
• Add sample application which uses paramconfig to fetch the configuration from Parameter Manager.
• Add the documentation to reflect the new capabilities of paramconfig

More information about parameter manager: https://cloud.google.com/secret-manager/parameter-manager/docs/overview

[suvidha-malaviya]

Opened the PR to add support for remote configuration with paramconfig module in Spring Cloud GCP using Parameter Manager Service: #3684