[Feature] Implement Global Stats Endpoint in API

[rahul-rocket]

Description:

We need to implement a new public endpoint in the Gauzy API to provide global statistics. This endpoint should aggregate data across all tenants and return key metrics in a JSON format. It should be accessible only if a specific environment variable FEATURE_OPEN_STATS is set to true. By default, this endpoint should be disabled.

Requirements:

1. Endpoint Details:

• Path: /api/stats/global
• Method: GET
• Visibility: Publicly accessible only if FEATURE_OPEN_STATS environment variable is set to true.

2. Environment Variable Configuration:

• Add an environment variable named FEATURE_OPEN_STATS with the default value set to false.
• If FEATURE_OPEN_STATS is set to true, the endpoint should be enabled and accessible publicly.
• Ensure proper handling of the environment variable to prevent exposure when not explicitly enabled.

3. Metrics to Include:

• Hours Tracked (hours): Total number of hours tracked across all tenants. This should be calculated from all time logs, considering their exact duration rather than fixed slot lengths.
• Invoices (invoices): Total number of invoices generated across all tenants.
• Employees (employees): Total number of employees across all tenants.
• Organizations (organizations): Total number of organizations in the system.
• Tenants (tenants): Total number of tenants.
• Expenses (expenses): Total amount of expenses recorded.
• Income (income): Total income generated.
• Tasks (tasks): Total number of tasks recorded.

4. Response Format:

{
"hours": "2343354",
"invoices": 3343,
"employees": 43545,
"organizations": 454,
"tenants": 4545,
"expenses": 454645,
"income": 67676,
"tasks": 12345
}

Note: Include data for all entities, including archived and deleted records.