fix: handle encoded commas in URL query parameters

[eth2353]

Motivation

The Teku validator client is unable to fetch validator statuses from a Lodestar beacon node if more than 1 validator status is requested due to the way they request the data. Lodestar should be able to serve Teku's requests.

Description

The issue is caused by the differing ways the validator clients encode the query parameter values.

Lodestar VC request:

GET /eth/v1/beacon/states/head/validators?id=0x978e96b6b6b474f3f91b705a311906b14a5e2893d15e01f5a0ff210393ace5e0abc8488e844dab00f430364ba4c19b1a&id=0x99f013b0314981b0083e494bdd2989304f9fc9dfd2b0c23b40429d817b02acc78f0b4328e45e745a5c6cc48e8f0e9930 HTTP/1.1

Teku VC request:

GET /eth/v1/beacon/states/head/validators?id=0x978e96b6b6b474f3f91b705a311906b14a5e2893d15e01f5a0ff210393ace5e0abc8488e844dab00f430364ba4c19b1a%2C0x99f013b0314981b0083e494bdd2989304f9fc9dfd2b0c23b40429d817b02acc78f0b4328e45e745a5c6cc48e8f0e9930 HTTP/1.1
-> the comma is URI-encoded as %2C . Lodestar then returns an empty array of validator statuses, resulting in Teku VC error messages (and the Teku VC therefore not starting validator duties for the affected validators):

19:14:03.083 WARN  - Unable to retrieve status for validator 978e96b.
19:14:03.083 WARN  - Unable to retrieve status for validator 99f013b.

I did not test other VC clients but it is possible others do the same.
The Beacon API Swagger seems to result in the comma unencoded in the request.

After reading some discussions on this topic, I am still unsure about which way should be considered technically correct and therefore decided to try supporting both ways on the Lodestar side.

This PR implements support for URI-encoded query parameter values, like the ones Teku VC sends. It is backwards compatible - it supports the comma encoded but also unencoded.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[nflaig]

Thanks for looking into this. There has been discussion on this topic in a previous issue #5403. As per RFC 3986, handling %2C as a delimiter is not correct, see #5403 (comment) for more detailed explanation.

[eth2353]

Thanks for your quick response, I thought I had checked everywhere but I did somehow miss this issue. I was not able to find any more follow-up discussion in the R&D discord. I've opened Consensys/teku#7757 in Teku's repository which fixes it from the other side.

[nflaig]

Thanks for opening the issue on Teku side, let's continue the discussion there if required.