KTOR-6412: add AcceptEncoding constants

[anton-erofeev]

Subsystem
http

Motivation
https://youtrack.jetbrains.com/issue/KTOR-6412

Solution
Added Accept Encoding constants

[e5l]

@marychatte, could you please check?

[marychatte]

Thanks for PR!
It's a good idea to add constants! Maybe we can use HeaderValueWithParameters as it's done already with ContentType. Because it is also can be a parameter ;q= (qvalues weighting). And please add Kdoc and some tests

[anton-erofeev]

Thanks for PR! It's a good idea to add constants! Maybe we can use HeaderValueWithParameters as it's done already with ContentType. Because it is also can be a parameter ;q= (qvalues weighting). And please add Kdoc and some tests

Hi @marychatte!
I updated the PR with review points fixes, could you please take a look?

[marychatte]

@anton-erofeev Good work on the PR! Thank you a lot
I added a few comments, but in general I think everything is good!

[marychatte]

small: maybe change such as "gzip", "compress", or "br" to such as "gzip", "compress", "br", etc.

[marychatte]

What do you think about having names capitalized? We have for example, ContentType.Application.Any for consistency we can have AcceptEncoding.Gzip

[marychatte]

Can we also add the next constructor:

public constructor(acceptEncoding: String, qValue: Double) : this(
        acceptEncoding,
        listOf(HeaderValueParam("q", qValue.toString()))
    )

So we can have for example AcceptEncoding("gzip", 0.2) and use it also here return AcceptEncoding(acceptEncoding, qValue)

[marychatte]

What do you think about adding the function match? To have something like this:
AcceptEncoding.Gzip.match(AcceptEncoding.All)

[marychatte]

Good work, thank you!
I will merge the PR when checks pass