[APPSEC-11887] Add Telemetry metric support

[GustavoCaso]

What does this PR do?

Adds support for telemetry metrics.

Telemetrics metrics is enabled by default and can be configured using c.telemetry.metrics = <bool> or using DD_TELEMETRY_METRICS_ENABLED

Each product will be able to send metrics using a straightforward API.

telemetry_client.add_<metric_type>_metric(namespace ["tracers", "general", "telemetry", "iast", "appsec"], metric_key String, value Numeric, tags Hash)

The metrics will be flushed at the interval configured for telemetry. I decided to reuse the same interval as telemetry to avoid having too many configurations for telemetry, also the RFC did not specify anything about this particular option.

Motivation:

Additional Notes:

How to test the change?

For Datadog employees:

• [ ] If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• [ ] This PR doesn't touch any of that.

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