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:

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 process the request
fga-client.credentials.request	Counter	The total number of times a new token was requested when using ClientCredentials

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
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 users
http.status_code	int	The status code of the response
http.method	string	The HTTP method for the request
http.host	string	Host identifier of the origin the request was sent to

We're implementing this using opentelemetry-api, which means that all actions will be a no-op unless an opentelemetry-sdk (or equivalent) instance is configured within an application. This is currently in draft as we work through the implementation across SDKs, but we're looking for any feedback folks may have!

References

Closes #92

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 81.28655% with 32 lines in your changes missing coverage. Please review.

Project coverage is 29.20%. Comparing base (fcb256c) to head (4159d51).

Files	Patch %	Lines
...ain/java/dev/openfga/sdk/telemetry/Attributes.java	57.89%	13 Missing and 3 partials ⚠️
...dev/openfga/sdk/api/client/HttpRequestAttempt.java	77.41%	6 Missing and 1 partial ⚠️
...c/main/java/dev/openfga/sdk/telemetry/Metrics.java	83.87%	2 Missing and 3 partials ⚠️
...in/java/dev/openfga/sdk/api/auth/OAuth2Client.java	71.42%	2 Missing ⚠️
.../main/java/dev/openfga/sdk/telemetry/Counters.java	50.00%	1 Missing ⚠️
...ain/java/dev/openfga/sdk/telemetry/Histograms.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #94      +/-   ##
============================================
+ Coverage     27.72%   29.20%   +1.48%     
- Complexity      785      815      +30     
============================================
  Files           158      166       +8     
  Lines          5862     6030     +168     
  Branches        639      650      +11     
============================================
+ Hits           1625     1761     +136     
- Misses         4161     4186      +25     
- Partials         76       83       +7     

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[evansims]

I'll do a follow-up PR adding documentation generated from the SDK Generator implementation, should this work be approved.