feat: support OpenTelemetry metrics

[evansims]

Description

Introduces OpenTelemetry metrics reporting into the SDK for specific actions. We're intentionally starting with only a few metric events that we can then grow over time.

We don't have any formal documentation for this currently. We'll write this as we roll it out across all SDKs, so here is a summary of the events and the associated attributes:

Supported Metrics

Metric Name	Type	Description
fga-client.request.duration	Histogram	The total request time for FGA requests
fga-client.query.duration	Histogram	The amount of time the FGA server took to internally process nd evaluate the request
fga-client.credentials.request	Counter	The total number of times a new token was requested when using ClientCredentials

Supported attributes

Attribute Name	Type	Description
fga-client.response.model_id	string	The authorization model ID that the FGA server used
fga-client.request.method	string	The FGA method/action that was performed (e.g. check, listObjects, ...) in camelCase
fga-client.request.store_id	string	The store ID that was sent as part of the request
fga-client.request.model_id	string	The authorization model ID that was sent as part of the request, if any
fga-client.request.client_id	string	The client ID associated with the request, if any
fga-client.user	string	The user that is associated with the action of the request for check and list objects
fga-client.request.retries	int	The number of retries attempted (starting from 1 for the original request). Deprecated, use http.request.resend_count
http.request.resend_count	int	The number of retries attempted (starting from 1 for the original request)
http.status_code	int	The status code of the response. Deprecated, use http.response.status_code
http.response.status_code	int	The status code of the response
http.method	string	The HTTP method for the request. Deprecated, use http.request.method
http.request.method	string	The HTTP method for the request
http.host	string	Host identifier of the origin the request was sent to
url.scheme	string	HTTP Scheme of the request (http/https)
url.full	string	Full URL of the request
user_agent.original	string	User Agent used in the query
http.client.request.duration	int	The total request time for FGA requests
http.server.request.duration	int	The amount of time the FGA server took to internally process nd evaluate the request

References

Closes #105

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.11029% with 217 lines in your changes missing coverage. Please review.

Project coverage is 25.45%. Comparing base (d1fa227) to head (16bb77c).

Files	Patch %	Lines
api_open_fga.go	55.55%	110 Missing and 10 partials ⚠️
internal/telemetry/attributes.go	34.09%	84 Missing and 3 partials ⚠️
internal/telemetry/telemetry.go	89.47%	2 Missing and 2 partials ⚠️
oauth2/internal/token.go	0.00%	3 Missing and 1 partial ⚠️
credentials/credentials.go	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   23.58%   25.45%   +1.87%     
==========================================
  Files          95      102       +7     
  Lines       10033    10576     +543     
==========================================
+ Hits         2366     2692     +326     
- Misses       7412     7612     +200     
- Partials      255      272      +17     

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[rhamzeh]

This does not yet implement fga_client.user right?

[evansims]

This does not yet implement fga_client.user right?

Correct, I haven't quite figured out how to approach that yet

This is now supported 😄