Add new subscriptions list, connect and disconnect

[wscourge]

Deprecated Methods:

• Subscription::all() - triggers E_USER_DEPRECATED warning
• Subscription::connect() - triggers E_USER_DEPRECATED warning
• Subscription::disconnect() - triggers E_USER_DEPRECATED warning

New Methods in ChartMogul\Metrics\Customers\Subscription:

• connect($dataSourceUUID, $customerUUID, array $subscriptions) - accepts only Metrics\Customers\Subscription instances
• disconnect($dataSourceUUID, $customerUUID, array $subscriptions) - accepts only Metrics\Customers\Subscription instances

[Copilot]

Pull request overview

This PR deprecates existing subscription methods and introduces new recommended static methods for connecting and disconnecting subscriptions, promoting better API design with static factory methods in the Metrics namespace.

Key Changes:

• Deprecated Subscription::all(), connect(), and disconnect() instance methods
• Added new static connect() and disconnect() methods to Metrics\Customers\Subscription
• Updated documentation to reflect recommended usage patterns

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/Subscription.php	Deprecated all(), connect(), and disconnect() methods with appropriate warnings
src/Metrics/Customers/Subscription.php	Added new static connect() and disconnect() methods as replacements
README.md	Updated documentation to show recommended vs deprecated usage patterns

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