suggested feature:Prepared `GenerateJwtToken` Method

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

Currently, developers need to manually generate JWT tokens by creating a custom method that includes the necessary claims and signing credentials. This process can be repetitive and prone to errors if not done correctly.

### Describe the solution you'd like

Introduce a `GenerateJwtTokenAsync` method in the `SignInManager` class that automatically generates a JWT token with the necessary claims and signing credentials. The method should take parameters similar to `SignInManager.SignInAsync`, such as the user object and additional claims.

**Example Code:**

```csharp
public class JwtService
{
private readonly UserManager _userManager;
private readonly IConfiguration _configuration;

public JwtService(UserManager userManager, IConfiguration configuration)
{
_userManager = userManager;
_configuration = configuration;
}

public async Task GenerateJwtTokenAsync(ApplicationUser user, IList additionalClaims = null)
{
var userClaims = await _userManager.GetClaimsAsync(user);
var claims = new List
{
new Claim(JwtRegisteredClaimNames.Sub, user.UserName),
new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
new Claim(ClaimTypes.NameIdentifier, user.Id)
};
claims.AddRange(userClaims);
if (additionalClaims != null)
{
claims.AddRange(additionalClaims);
}

var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_configuration["Jwt:Key"]));
var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

var token = new JwtSecurityToken(
issuer: _configuration["Jwt:Issuer"],
audience: _configuration["Jwt:Audience"],
claims: claims,
expires: DateTime.Now.AddMinutes(30),
signingCredentials: creds);

return new JwtSecurityTokenHandler().WriteToken(token);
}
}
```

### Additional context

*Benefits:**

- Simplifies the process of generating JWT tokens by providing a built-in method.
- Ensures consistency and security in JWT token generation across applications.
- Reduces the likelihood of misconfiguration and potential security vulnerabilities.
- Provides a similar level of convenience as the `SignInManager.SignInAsync` method for cookie-based authentication.

**Additional Context:**

This feature request is inspired by the convenience and security provided by the `SignInManager.SignInAsync` method for cookie-based authentication. Having a similar method for JWT authentication would provide a consistent and secure experience for developers.