Sentry Metrics for Native

[JoshuaMoelans]

Closely related to #1210 , we are soon to be adding Metrics as a new type of telemetry for our SDKs.

These look somewhat similar to logs, but only take in name, value, options. They follow the same batching logic (flushing every 100 metrics/5s, have the same default attributes, and a before_send_metric hook to filter/modify metrics.

https://develop.sentry.dev/sdk/telemetry/metrics/

Related work:

• Sentry Structured Logging for Native (C/C++) #1210 <- contains the logs batching implementation (to be re-used for metrics)
• Structured Logs: follow up - custom attributes #1405 <- introduction of attributes
• Implement Global Attributes API #1448 <- global attributes should be applied to metrics as well

[linear]

NATIVE-145