Added supervisor init telemetry event

[akoutmos]

I am currently working on the PromEx Broadway plugin (akoutmos/prom_ex#39) and would like to incorporate some of the configuration details into the Broadway Grafana dashboard. Thoughts on surfacing the config from the Topology module after the supervisor is started?

If you are okay with this approach I will go through and add the necessary documentation to the telemetry events. Thanks in advance!

[coveralls]

Pull Request Test Coverage Report for Build 778087c8823a988031750c90b547000269a981a7-PR-223

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 15 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.06%) to 94.885%

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Files with Coverage Reduction	New Missed Lines	%
lib/broadway/topology/producer_stage.ex	15	86.32%

Totals
Change from base Build 05f1dfc3461730a57e7942c4b623f3d70e56163e:	0.06%
Covered Lines:	538
Relevant Lines:	567

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💛 - Coveralls

[josevalim]

Hi @akoutmos! This looks good to me but I am afraid the configuration is somewhat private. We may tweak it so it mirrors our internals and that may break the dashboard. We should either expose specific information that you need or expose the user supplied map as is.

[akoutmos]

I'm ok with using the user supplied map as opposed to the internal representation. It looks like the user's options are going through NimbleOptions so there shouldn't be a case where they think they set something, PromEx reports that something was set, but it turns out that their setting was ignored due to invalid option structure.

I'll update the PR to leverage the user options and also update the telemetry docs to include this new event. Thanks for the speedy feedback!

[akoutmos]

Updated the PR to address your feedback. Let me know if there is anything else that i should adjust :).

[philss]

Great addition!
I left one suggestion :)

[philss]

Just a nitpick: instead of supervisor, we could name this topology or pipeline for better proximity with naming from Broadway. WDYT?

[akoutmos]

Great idea! I liked topology better and updated the PR with that one :D

[josevalim]

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