Use tracing fields to store variable log data

[NickCaplinger]

Hey again!

This PR goes through all of the places that the crate uses tracing events and pushes all of the variable data into fields.

This is something that we recently did for our backend services, and it made it far easier to analyze our logs using Google's Log Analytics tool. We're also able to easily pull out data from these fields, which is helpful not only for Log Analytics, but for log-based metrics!

We actually run our services with debug-level logging enabled for the firestore crate in order to get better insight into the behavior and performance of the database, and track down cases of transaction contention, which is why I've made this PR.

The root-level documentation of tracing has additional explanation of the merits of using fields here.

Below is an example of what this looks like in Log Analytics for one of our services. This maybe isn't the best example because I've picked a small sample so I didn't have to draw so many black boxes, but you can see where some firestore events haven't been grouped.

Thank you for your continued, high quality work on this project!

[abdolence]

Hey, first of all, you don't have to convince me that structured tracing/logging is great :)
As you can see I already implemented spans for tracing with some attributes, and logs was missing structured fields indeed.

When I started this crate it was actually using old log crate which didn't have an ability to propagate normally fields, and then I just haven't changed it yet, so I really appreciate your help in this area 🏆

Generally it looks good, but I need a bit more time to review when I have time, so I'll come back to you.

[abdolence]

PS Also it fails on tests/compilation in pipelines :)

[NickCaplinger]

Hey, first of all, you don't have to convince me that structured tracing/logging is great :)
As you can see I already implemented spans for tracing with some attributes, and logs was missing structured fields indeed.

When I started this crate it was actually using old log crate which didn't have an ability to propagate normally fields, and then I just haven't changed it yet, so I really appreciate your help in this area 🏆

This is exactly what happened to us, so I completely understand!

Generally it looks good, but I need a bit more time to review when I have time, so I'll come back to you.

Absolutely! Given the nature of the PR, it's not exactly urgent.

Thanks again. :)

[abdolence]

Hey, it still doesn't compile for me :)

[abdolence]

I'm trying to test all the features enabled:

cargo test --all-features

[NickCaplinger]

Yikes, sorry about that!

[abdolence]

In some places, it looks a bit now repetitive since we have tracing spans, etc:

Firestore Get Doc{/firestore/collection_name="integration-test-childs" /firestore/document_name="projects/latestbit/databases/(default)/documents/integration-nested-test/test-parent/integration-test-childs/test-child" /firestore/response_time=125}: firestore::db::get: Read document. document_path="projects/latestbit/databases/(default)/documents/integration-nested-test/test-parent/integration-test-childs/test-child" duration_milliseconds=125

I guess for some cases some people might want both, so I'll leave it for now.

I'm going to merge this, thanks for contributions! 👍🏻