Connect hook

[pfreixes]

Addresses #1786

Added a new PoolHook interface allowing the user to add two new hooks that would be called before and after the creation of a connection, allowing the user - among other stuff - to measure the connection latency.

User still uses the AddHook interface but providing an extended interface which supports the two methods required by the pool.

An example can be found here https://github.com/go-redis/redis/pull/1803/files#diff-ee4b7901a404913de455c4b45c583a3d0bf51e6c3abc06c93c2a1fa6c3eac235R16

What is missing

Does not support the clone behaviour used by functions like Client.WithTimeout which for the client hooks it creates a list by using a shallow copy, decoupling hooks from the former and the new cloned client.

Current proposal does not support this, since the pool is shared by all of the cloned clients.

[vmihailenco]

Have you considered using OpenTelemetry Metrics to measure the data you need? We already have some metrics and probably should not wait for a stable release to add more.

I understand that the more hooks the better, but this PR adds considerable amount of code and complexity.

[pfreixes]

We are already measuring op latency and errors by using the current hooks, which I guess is what OpenTelemetry would provide. I would like to make and step forward and also measure create connection latency.

If this PR does not not move forward, we will do that by overriding the dialer.

[vmihailenco]

👍 I just meant that OpenTelemetry should work (at least in theory) with Prometheus/Grafana/whatever. So may be adding it to your stack could help.

[pfreixes]

Ill close the PR, if eventually other users are interested we can reborn this.

[vmihailenco]

Sounds good - thanks 👍