Adding ready route to inputs.influxdb_v2_listener

[eraac]

Required for all PRs:

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

Following this discussion #7828 (comment), that can be great if this come with 1.16

All credits for @magichair, I only revert the commit who remove the ready route

Thanks!

[ssoroka]

this endpoint is deprecated and was specifically removed. Any comments on why it should be added back in?

[magichair]

@ssoroka is there a deprecation note I'm missing? https://docs.influxdata.com/influxdb/v2.0/api/#tag/Ready still looks fully formed and planned for InfluxDB v2. The original "removal" was more a "don't put it in the first version of this plugin if we don't need it"-type choice.

[ssoroka]

Perhaps I misunderstood. I was under the impression it's not used anymore, so I'm curious where this use case is coming from. I'm not against adding this in. Nevermind. This is supported by InfluxDB and there's no reason not to proxy support for the request.