Support unique groups

[DenuxPlays]

Hey,
I recently wanted to use a unique group but I don't think that sea-orm supports that.
Here is the PostgreSQL documentation: https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-UNIQUE-CONSTRAINTS

And here is an sql example:

CREATE TABLE users
(
    id                         BIGINT PRIMARY KEY,
    email                      TEXT                     NOT NULL UNIQUE,
    name                       TEXT                     NOT NULL,
    flags                      INTEGER                  NOT NULL,
    password                   TEXT                     NOT NULL,
    reset_token                TEXT,
    reset_sent_at              timestamp with time zone,
    email_verification_token   TEXT,
    email_verification_sent_at timestamp with time zone,
    email_verified_at          timestamp with time zone,
    created_at                 timestamp with time zone NOT NULL,
    updated_at                 timestamp with time zone NOT NULL,
    UNIQUE (email, email_verification_token),
    UNIQUE (email, reset_token)
);

[DenuxPlays]

Maybe the user code could look something like this:

#[derive(Clone, Debug, PartialEq, DeriveEntityModel, Eq, Serialize, Deserialize)]
#[sea_orm(table_name = "users")]
pub struct Model {
    #[sea_orm(primary_key, auto_increment = false)]
    pub id: i64,
    #[sea_orm(column_type = "Text", unique, unique_group("email-email_verification_token", "email-reset_token"))]
    pub email: String,
    #[sea_orm(column_type = "Text")]
    pub name: String,
    pub flags: i32,
    #[sea_orm(column_type = "Text")]
    pub password: String,
    #[sea_orm(column_type = "Text", nullable, unique_group("email-reset_token"))]
    pub reset_token: Option<String>,
    pub reset_sent_at: Option<DateTimeWithTimeZone>,
    #[sea_orm(column_type = "Text", nullable, unique_group("email-email_verification_token"))]
    pub email_verification_token: Option<String>,
    pub email_verification_sent_at: Option<DateTimeWithTimeZone>,
    pub email_verified_at: Option<DateTimeWithTimeZone>,
    pub created_at: DateTimeWithTimeZone,
    pub updated_at: DateTimeWithTimeZone,
}