feat(): add support for manual init

[Junikorn]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Motivation for no tests:
I searched repository for proper place to add tests for this feature but none seem to be correct (there are only e2e tests with specific convention).
I run e2e suite though and it passes.
I also tested the feature manually on my usecase (on and off).
Please suggest test convention if you want me to write tests for this feature and I will do my best to apply it.

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

There is no option to disable DataSource initialization during module initialization

Issue Number: 1762

What is the new behavior?

Option manualInitialization was added to TypeOrmModuleOptions interface.
Module does not initialize database if option is set to true.

Does this PR introduce a breaking change?

• Yes
• No

Other information

I have done one minor refactor to limit logic repetition

[cjam]

Anything holding this back from getting merged in? I could definitely make use of it.

[kamilmysliwiec]

LGTM

[callumjg]

Any indication when this change might be published to npm?

[Woodz]

Any indication when this change might be published to npm?

Looks like it was release in v10.0.1

[callumjg]

Any indication when this change might be published to npm?

Looks like it was release in v10.0.1

The same day as my comment! Was maybe a day early 😮‍💨