feat: Added support for templates in external secrets

[pawan-mehta-dt]

Description

Added support for subPath and templates in external secrets

Fixes #5861

How Has This Been Tested?

• [x] Tested on separate devtron instance

Checklist:

• [x] The title of the PR states what changed and the related issues number (used for the release note).
• [ ] Does this PR requires documentation updates?
• [ ] I've updated documentation as required by this PR.
• [x] I have performed a self-review of my own code.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have tested it for all user roles.
• [ ] I have added all the required unit/api test cases.