✨ feat: add Delete method to Store struct in session middleware

[kaptinlin]

Description

This pull request introduces a new Delete method to the Store struct in the Fiber's session middleware. The Delete method is designed to delete a specific session id from the storage.

The motivation behind this change is to provide more control over individual session management, especially in scenarios like administrator-enforced user logout or user-initiated logout from a specific device session. With the Delete method, we can easily delete a specific session, providing a more efficient and flexible way to manage individual user sessions.

This pull request also includes relevant test code to ensure the correct functionality of the Delete method.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• For new functionalities I follow the inspiration of the express js framework and built them similar in usage
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation - /docs/ directory for https://docs.gofiber.io/
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• If new dependencies exist, I have checked that they are really necessary and agreed with the maintainers/community (we want to have as few dependencies as possible)
• I tried to make my code as fast as possible with as few allocations as possible
• For new code I have written benchmarks so that they can be analyzed and improved

Usage

app.Post("/admin/session/:id/logout", func(c *fiber.Ctx) error {
    // Get session id from request
    sessionID := c.Params("id")

    // Delete the session
    if err := store.Delete(sessionID); err != nil {
        return c.Status(500).SendString(err.Error())
    }

    return c.SendString("Logout successful")
})

[ReneWerner87]

@kaptinlin pls check the review comments

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