[x.json2] Add skippable struct fields @[json: '-']

[johnpgr]

Describe the feature

The main json module has a skippable struct fields feature, so fields on the struct don't get encoded / decoded

struct Foo {
    x int @[json: '-'] // This field doesn't get encoded/decoded
    y int
    z int    
}

Use Case

I wanted a way to encode a struct that didn't envolve mapping it to another struct, because only one field had to be hidden from json.
I could've used the main json module, but the way it encodes time.Time as a number doesn't work for me

Proposed Solution

Implement the @[json: '-'] attribute to skip struct fields

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

V 0.4.4 c9933da.10c2f9e

Environment details (OS name and version, etc.)

OS: linux, Ubuntu 22.04.3 LTS (WSL 2)

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[johnpgr]

I can work on this