docs(v1): add comprehensive configuration references for app and piped

[shivansh-gohem]

What this PR does / Why we need it:

This PR provides the structured and updated v1 configuration references requested in the EPIC. It replaces the "work in progress" placeholders in the docs-v1.0.x directory with comprehensive, markdown-formatted tables mapped directly from the v1 Go structs (pkg/configv1/application.go and pkg/configv1/piped.go).

Key Documentation Updates:

1. Application Configuration (app.config):

   • Documented the shift to the unified Application kind.
   • Added the requirement for the pipecd.dev/platform label.
   • Mapped all core v1 deployment specs (planner, pipeline, trigger, etc.).

2. Piped Configuration (piped.config):

   • Documented the new plugin-based architecture.
   • Replaced legacy platformProviders with the new plugins and nested deployTargets specifications.
   • Added structured tables for internal configs like Git, SecretManagement, and Notifications.

Which issue(s) this PR fixes:

Fixes #6542