Support migrations files with ts file extension

[kroleg]

Pull Request check-list

Please make sure to review and check all of these items:

• Does npm run test pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
• Have you added new tests to prevent regressions?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

Description of change

Support *.ts migration files

[sushantdhiman]

Released as https://github.com/sequelize/cli/releases/tag/v6.2.0

[intellix]

I can't create feature requests without a test case but don't wanna lose the idea so writing here instead.

My current migrations are all JS and would like to transition them to TS migrations so I can import the interfaces to understand the methods available. They're being read but my migrations are starting from scratch and it seems to be because the migration name includes the extension:

20181113051813-create-achievement.js
20181113051813-create-achievement.ts

I can run an SQL to change the migrated extensions I guess:

UPDATE "SequelizeMeta" SET "name" = REPLACE("name", '.js', '.ts')

Would be cool if the migration name didn't include the extension (as an option) to allow users to move freely between extensions: js -> mjs -> cjs -> ts

[mirajehossain]

How do I generate migration in .ts extension?
Please update the doc and give an example to use this feature thanks.