Add support for Identity-Based Pricing

[dangtony98]

Description 📣

This PR adds support for identity-based pricing.

Logic: In order to implement identity-based pricing, we create a new price in Stripe with seat_type metadata (can be either user or identity). When Infisical fetches back the feature set from the license server, the license server computes identitiesUsed and has identityLimit based on the Stripe product + metadata on the price. The Infisical platform then imposes the necessary constraints at the frontend UI-level and backend.

Included in this PR:

• If identityLimit is specified in the customer's feature set, then checks are imposed for example when inviting a new user to an organization or when a new user logs into an organization via SAML / LDAP.
• When users are added/removed from an organization, Infisical updates the license server with the new member and identity counts.

Note: Existing users of Infisical are not affected by the price change; only new users that will be bound to the identity-based prices on Stripe.

Type ✨

• Bug fix
• New feature
• Breaking change
• Documentation

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