feat(ws): introduce message parser for ws adapter

[CodyTseng]

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• 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)
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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?

Issue Number: #14027

What is the new behavior?

Add a setMessagePreprocessor method to the wsAdapter to customize how messages are preprocessed.

const wsAdapter = new WsAdapter(app);

wsAdapter.setMessagePreprocessor((message: any) => {
  const [event, ...data] = message;
  return { event, data };
});

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build c2aa204b-3107-4901-82ec-903bb6861111

Details

• 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 92.243%

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Totals
Change from base Build 72f148bc-4145-44b3-a3c4-06a616307114:	0.0%
Covered Lines:	6754
Relevant Lines:	7322

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💛 - Coveralls

[kamilmysliwiec]

I wonder if we should move the "JSON.parse" call to the preprocessor, and just call it parser instead?

[CodyTseng]

It's a great idea.

Additionally, should we consider supporting configuration in the constructor, like this:

new WsAdapter(app, {
  messageParser: (data) => ...
})

[kamilmysliwiec]

sure, sounds good!

[kamilmysliwiec]

LGTM