[Improvement]: Move to OC based secret management without relying on specific key vault

[menakaj]

Please select the area the issue is related to

Area/Agent Lifecycle (Agent create, configure, kinds, build, test, deploy, keys/tokens)

Please select the aspect the issue is related to

Aspect/Agent Configuration (Agent configuration, kinds, build options)

Suggested Improvement

Currently Agent manager strictly relies on openbao as the key vault.
But, this impose complications when going to support different key vault products since, we need to implement individual kv clients.

Solution:
Integrate into the secret management capability offered by open-choreo. OC supports ESO based secret sync pattern, which allows storing secrets in KV. This provides us with the capability to integrate with any key vault solution, supported by ESO.

Related Issues

No response

[hanzjk]

PR #1327. Moves our custom Secret Manager implementation to OpenChoreo from OpenBao.

But, OpenBao KV is still called directly in the following two scenarios:

1. Agent IDP Thunder provisioning
2. Git secrets for private repositories: Git credentials are stored in KV through the OpenChoreo APIs. However, operations such as listing commits require retrieving the credentials by calling OpenBao KV directly.