Fix Create Data Type section in 02-writing-migration.md

[lynxlevin]

This is to fix 2 compile errors.

• Add Type import to fix the following error:
  • error[E0433]: failed to resolve: use of undeclared type Type
• Add to_owned() method to fix the following error:
  • expected TypeCreateStatement, found &mut TypeCreateStatement

Changes

• Fixes 2 compile errors in sample code in document.

[lynxlevin]

Sea-orm version

[dependencies.sea-orm-migration]
version = "~1.0"
features = [
  # Enable at least one `ASYNC_RUNTIME` and `DATABASE_DRIVER` feature if you want to run migration via CLI.
  # View the list of supported features at https://www.sea-ql.org/SeaORM/docs/install-and-config/database-and-async-runtime.
  # e.g.
  "runtime-tokio-native-tls", # `ASYNC_RUNTIME` feature
  "sqlx-postgres",            # `DATABASE_DRIVER` feature
  "with-uuid",
  "with-chrono",
  "with-json",
]

[lynxlevin]

About the first error.
Code

use sea_orm::{EnumIter, Iterable};
use sea_orm_migration::prelude::*;

#[derive(DeriveMigrationName)]
pub struct Migration;

#[async_trait::async_trait]
impl MigrationTrait for Migration {
    async fn up(&self, manager: &SchemaManager) -> Result<(), DbErr> {
        manager
            .create_type(
                Type::create()
                    .as_enum(TimezoneEnum)
                    .values(TimezoneVariants::iter()),
            )
            .await
    }
}

#[derive(DeriveIden)]
struct TimezoneEnum;

#[derive(DeriveIden, EnumIter)]
pub enum TimezoneVariants {
    #[sea_orm(iden = "Asia/Tokyo")]
    AsiaTokyo,
    #[sea_orm(iden = "UTC")]
    Utc,
}

Error message on sea-orm-cli migrate fresh

Running `cargo run --manifest-path ./migration/Cargo.toml -- fresh -u postgresql://test_user:xxxxxx@localhost:5432/test`
   Compiling migration v0.1.0 (/migration)
error[E0433]: failed to resolve: use of undeclared type `Type`
  --> src/m20240926_000001_create_users_table.rs:12:17
   |
12 |                 Type::create()
   |                 ^^^^ use of undeclared type `Type`
   |
help: consider importing one of these items
   |
1  + use crate::extension::postgres::Type;
   |
1  + use sea_orm_migration::prelude::extension::postgres::Type;
   |

For more information about this error, try `rustc --explain E0433`.
error: could not compile `migration` (lib) due to 1 previous error
Fail to run migration

[lynxlevin]

The second error.
Code:

use sea_orm_migration::prelude::extension::postgres::Type;
// No other changes to the code above.

Error:

Running `cargo run --manifest-path ./migration/Cargo.toml -- fresh -u postgresql://test_user:xxxxxx@localhost:5432/test`
   Compiling migration v0.1.0 (/migration)
error[E0308]: mismatched types
  --> src/m20240926_000001_create_users_table.rs:13:17
   |
12 |               .create_type(
   |                ----------- arguments to this method are incorrect
13 | /                 Type::create()
14 | |                     .as_enum(TimezoneEnum)
15 | |                     .values(TimezoneVariants::iter()),
   | |_____________________________________________________^ expected `TypeCreateStatement`, found `&mut TypeCreateStatement`
   |
note: method defined here
  --> /.cargo/registry/src/index.crates.io-6f17d22bba15001f/sea-orm-migration-1.0.0/src/manager.rs:57:18
   |
57 |     pub async fn create_type(&self, stmt: TypeCreateStatement) -> Result<(), DbErr> {
   |                  ^^^^^^^^^^^

For more information about this error, try `rustc --explain E0308`.
error: could not compile `migration` (lib) due to 1 previous error
Fail to run migration