Model secrets as a property of PostgreSql Databases

[Reshrahim]

This pull request introduces changes to how PostgreSQL database credentials are managed and injected into Kubernetes containers using secrets. The changes refactor the postgreSqlDatabases resource to require a secretName property, ensuring that sensitive information like usernames and passwords is stored in Kubernetes secrets rather than as resource properties. The Bicep recipes, documentation, and schema definitions have been updated to reflect and support this new pattern.

Short gist - https://gist.github.com/Reshrahim/5ea332db690c623de64c1c85a01071aa

• Modified the postgreSqlDatabases resource schema to require the secretName property and removed username and password from the resource outputs and required properties.
• Refactored the PostgreSQL Bicep recipe to require a secretName property, removing username and password from output properties and instead sourcing them from a referenced Kubernetes secret. The deployment now pulls credentials using valueFrom.secretKeyRef referencing the provided secret.
• Updated the container connection logic to map secret keys (username, password) as uppercase environment variables when a secretName is provided, ensuring injection of credentials into containers. Also fixed this bug Environment variables from Connected resource doesn't get injected properly on the container #92
• Updated developer documentation in both the PostgreSQL and secrets resource types to demonstrate the new pattern of creating and referencing secrets, including deployment instructions and sample Bicep.
• Updated test app.bicep files to use the new secret-based pattern for PostgreSQL databases and secrets

[zachcasper]

I only reviewed secrets.yaml, postgreSqlDatabases.yaml, and postgresql.bicep.

[zachcasper]

Needs to be

          connections: {
            postgresql: {
              source: postgresql.id

[zachcasper]

Suggested change

	secretName:
	type: string
	description: "(Required) The name of the secret containing the database crdentials"
	secretName:
	type: string
	description: "(Required) The name of the secret containing the database crdentials"

I'm wondering if this should be credentials.secretName rather than just secretName. If that clearer?

[zachcasper]

Suggested change

	var port = 5432
	var port = 5432
	var applicationName = context.application != null ? context.application.name : ''
	// Extract last segment from environment path for labels
	var environmentId = resourceProperties.?environment ?? ''
	var environmentParts = environmentId != '' ? split(environmentId, '/') : []
	var environmentName = length(environmentParts) > 0
	? environmentParts[length(environmentParts) - 1]
	: ''
	// Extract resource group name
	// Index 4 is the resource group name
	var resourceGroupName = split(context.resource.id, '/')[4]
	// Common labels
	var labels = {
	'radapp.io/resource': resourceName
	'radapp.io/application': applicationName
	'radapp.io/environment': environmentName
	'radapp.io/resource-type': replace(context.resource.type, '/', '-')
	'radapp.io/resource-group': resourceGroupName
	}

[Reshrahim]

Should all of these be populated when deploying Recipes? I think we should prioritize this issue -#60 and not have users write so much code to get Radius metadata.

[zachcasper]

Suggested change

	namespace: namespace
	namespace: namespace
	labels: labels

[zachcasper]

Suggested change

	namespace: namespace
	namespace: namespace
	labels: labels

[Reshrahim]

@sk593 and @lakshmimsft - Can you help review updates to the container Recipe?