KIP-546 Client quota APIs

[agriffaut]

This PR implements the new ClientQuota API, available since Kafka 2.6.0.0

KIP: https://cwiki.apache.org/confluence/display/KAFKA/KIP-546%3A+Add+Client+Quota+APIs+to+the+Admin+Client

Protocols:
https://kafka.apache.org/protocol#The_Messages_DescribeClientQuotas
https://kafka.apache.org/protocol#The_Messages_AlterClientQuotas

[dnwe]

@agriffaut thanks for your contribution, this is great!

One question I had after an initial scan over the PR, was there a design goal around consistently using slices of pointers in the protocol definitions here? The slices will always either be empty or filled and will never have nil values, so I'm not sure why we wouldn't make these slices of the concrete type? As we (currently) have a strong coupling between the parameters for the high level functions in admin.go and the protocol structs, we similarly end up with map[string]*string etc.

[dnwe]

I rebased and it also looks like TestDescribeClientQuotasResponse might be flakey. Please could you take a look?

2021-05-05T22:41:43.7835979Z === RUN   TestDescribeClientQuotasResponse
2021-05-05T22:41:43.7836889Z     request_test.go:96: Encoding Multi Value failed
2021-05-05T22:41:43.7837592Z         got  [0 0 0 0 0 0 255 255 0 0 0 1 0 0 0 1 0 4 117 115 101 114 255 255 0 0 0 2 0 18 99 111 110 115 117 109 101 114 95 98 121 116 101 95 114 97 116 101 65 46 132 128 0 0 0 0 0 18 112 114 111 100 117 99 101 114 95 98 121 116 101 95 114 97 116 101 65 46 132 128 0 0 0 0] 
2021-05-05T22:41:43.7838308Z         want [0 0 0 0 0 0 255 255 0 0 0 1 0 0 0 1 0 4 117 115 101 114 255 255 0 0 0 2 0 18 112 114 111 100 117 99 101 114 95 98 121 116 101 95 114 97 116 101 65 46 132 128 0 0 0 0 0 18 99 111 110 115 117 109 101 114 95 98 121 116 101 95 114 97 116 101 65 46 132 128 0 0 0 0]
2021-05-05T22:41:43.7839480Z --- FAIL: TestDescribeClientQuotasResponse (0.00s)

[dnwe]

@agriffaut 👋 any thoughts on the above comments?

[agriffaut]

@dnwe I finally managed to work again on that PR, sorry for the delay.
As you said, some pointers were useless and have been removed !

Please tell me if this looks good to you!

[bai]

LGTM

[bai]

Thanks for your contribution @agriffaut.

I'll wait for dnwe to review before we ship this 🙏🏼

[dnwe]

LGTM. Thanks again for the PR and the updates 🙇

[bai]

Thanks @dnwe for reviewing 🙏🏼