Update prom client with support for UTF-8

[zeitlinger]

To avoid a breaking change

• a new flag has been introduced to opt-in to UTF-8 support: otel.exporter.prometheus.utf8 -> this is wrong
• we should use translation_strategy instead
  • see https://github.com/open-telemetry/opentelemetry-specification/issues/4634
  • requires https://github.com/prometheus/client_java/pull/1557

[codecov[bot]]

Codecov Report

:x: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 89.98%. Comparing base (63d4617) to head (4c214e3). :warning: Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ry/exporter/prometheus/PrometheusMetricReader.java	66.66%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7588      +/-   ##
============================================
- Coverage     89.99%   89.98%   -0.01%     
- Complexity     7079     7081       +2     
============================================
  Files           803      803              
  Lines         21412    21428      +16     
  Branches       2086     2087       +1     
============================================
+ Hits          19269    19282      +13     
- Misses         1479     1482       +3     
  Partials        664      664              

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[zeitlinger]

@jkwatson please have a look

[jkwatson]

no longer blocked by the spec?

[zeitlinger]

no longer blocked by the spec?

We talked in the spec meeting that it's up to the SDKs to decide if __ should be converted to _ or not.

So from that point of view, we're free to keep __ as is. However, I didn't want to introduce a breaking change (which is also SDK decision) - so I added a setting to enable UTF-8.

If

• otel.exporter.prometheus.utf8 is false, we shorten __ to _ (and %% becomes __ and then _)
• otel.exporter.prometheus.utf8 is true, the SDK passes all chars as is to the prom client - expecting that the user wants to keep that as is in the entire pipeline

We can decide that we're OK with the breaking change - and then we don't need this property.