GRPC: Fix credentials and introduce arguments

[sjkummer]

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)

PR Type

What kind of change does this PR introduce?

[x] 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?

GRPC credentials were completly ignored on client side. It was no more possible to establish a secure SSL GRPC-connection. Further, it was no more possible to pass GRPC-arguments

Issue Number: #4597

What is the new behavior?

GRPC-credentials work again (as they have in Nestjs6). Additionaly, an argument parameter was added to the GRPC options, to pass any of the arguments defined in https://grpc.github.io/grpc/core/group__grpc__arg__keys.html

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[coveralls]

Pull Request Test Coverage Report for Build 23046

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.632%

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Totals
Change from base Build 20728:	0.0%
Covered Lines:	4689
Relevant Lines:	4955

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💛 - Coveralls

[kamilmysliwiec]

What do you think about copying/mimicking options from this file:
https://github.com/grpc/grpc-node/blob/master/packages/grpc-js/src/channel-options.ts
instead of introducing a new loosely typed arguments property? Another solution would be to add [key: string]: any; to the GrpcOptions['options']

[kamilmysliwiec]

Since this fix is quite important, I'll push it as a separate commit

[sjkummer]

Hm, what about exporting the internally used grpc package? This will:

1. Allow typed GRPC-options for credentials, arguments and so on, without code duplication
2. This will avoid Type Errors, which occur if the Application does not use the exactly same GRPC version to create the credentials as Nestjs uses internally (this actually only works because npm dedups node_modules, see Generated client fails in Node on latest version grpc/grpc#10786 )

[kamilmysliwiec]

Although, I'd love to do it, grpc is an optional package and re-exporting types that come from the optional library will lead to compilation errors if skipLibCheck (in tsconfig) is set to true (which is the case for both starter project and CLI)

[sjkummer]

@kamilmysliwiec Finally, I've fixed the tests 😅

[kamilmysliwiec]

Thank you!

[kamilmysliwiec]

🤦 Just FYI: I've clicked "Close" by accident, but your PR has already been merged! I can't reopen now since the "These commits are already merged" shows up