feat(collections): add alternative value codec

[testinginprod]

Description

Closes: #16771

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[tac0turtle]

Could we get a few docs in this feature as well

[testinginprod]

Could we get a few docs in this feature as well

docs added 👍

[julienrbrt]

lgtm! However, I feel like the API does not convey immediately what it does.
I find the word “alternative”, while it is more a fallback, a bit confusing, just my two cents, however.

[testinginprod]

lgtm! However, I feel like the API does not convey immediately what it does. I find the word “alternative”, while it is more a fallback, a bit confusing, just my two cents, however.

We can change the name if you feel it does not express well its role. I'm open to suggestions!

[julienrbrt]

lgtm! However, I feel like the API does not convey immediately what it does. I find the word “alternative”, while it is more a fallback, a bit confusing, just my two cents, however.

We can change the name if you feel it does not express well its role. I'm open to suggestions!

I do not have a better suggestion 😅, it was simply not immediately clear for me what "alternative" meant by just reading the function arguments (without reading it or the godoc).

[testinginprod]

@julienrbrt I think we can merge as is, worst case we can break this API, anyways it's intended for super advanced use-cases so I don't think a regular developer will really have to deal with this.