Add support for Sentry Developer Metrics

[cleptric]

This adds support for Sentry Developer Metrics.

See getsentry/sentry#58584

use function Sentry\metrics;

// Add 4 to a counter named `hits`
metrics()->increment(key: 'hits', value: 4);

// Add 25 to a distribution named `response_time` with unit milliseconds
metrics()->distribution(key: 'response_time', value: 25, unit: MetricsUnit::millisecond());

// Add 2 to gauge named `parallel_requests`, tagged with `type: "a"`
metrics()->gauge(key: 'parallel_requests, value: 2, tags: ['type': 'a']);

// Add a user's email to a set named users.sessions, tagged with role admin
metrics()->set('users.sessions', 'jane.doe@example.com', null, ['role' => User::admin()]);

// Flush the metrics to Sentry
metrics()->flush();

// We recommend registering the flushing in a shutdown function
register_shutdown_function(static fn () => metrics()->flush());

In case you're not already enrolled on our Metrics alpha program, please # here.

To-Dos

• Add a metrics()->timing(fn () => doSomething(), ...) function https://develop.sentry.dev/sdk/metrics/#distributions
• Add key & tags normalization https://develop.sentry.dev/sdk/metrics/#normalization
• Add metric_code_locations option

[cleptric]

Marking as Draft again, missed some stuff

• The envelope should be serialized as statsd instead, it's more efficient https://getsentry.github.io/relay/relay_metrics/index.html#metric-envelopes
• All metric types should support units
• A custom string unit, like meter|inch etc. must also be supported
• Distribution values should allow strings as well, which need to be hashed with crc32
• We also should add some sort of aggregation, using 10 second buckets to not overwhelm the transport

[stayallive]

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