feat(graphql): add support for option newline at the end of schema file

[sabolch]

PR Checklist

Please check if your PR fulfills the following requirements:

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

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [X] 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?

Issue Number: #2732

What is the new behavior?

Added new option addNewlineAtEnd to BuildSchemaOptions, which appends a newline at the end of the generated GraphQL SDL file when set to true. If the option is set to false or omitted, the SDL file will be generated without adding an extra newline at the end. This option is applicable only in the code-first approach.

Does this PR introduce a breaking change?

• [ ] Yes
• [X] No

Other information

[kamilmysliwiec]

lgtm