feat(platform-fastify): add fastify custom log level feature

[daimalou]

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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?

can not close fastify buildin log

Issue Number: N/A https://github.com/nestjs/nest/issues/14137

use fastify 5

https://fastify.dev/docs/latest/Reference/Routes/#custom-log-level

What is the new behavior?

close fastify buildin log

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information