configurable limits on custom attributes

[richardelms]

Goal

implement configurable limits on custom attributes.

Logging

Part of the original task was to implement logging when an attribute is truncated or dropped. This has been broken out into it's own task because of the performance issues unity logging presents.

Changeset

• Added the new config values AttributeStringValueLimit , AttributeArrayLengthLimit and AttributeCountLimit
• String and array lengths in attributes are checked for truncation just before the span is serialised for delivery.
• The number of custom attributes in a span is checked when an attribute is added, the attribute is dropped if the limit is exceded.
• Added the attribute dropped_attributes_count
• Made sure that all calls to UnityEngine.Debug.Warning occur on the main thread.

Testing

Added unit and E2E tests

[bugsnagbot]

Build size impact

Format	Size impact of Bugsnag (kB)
IL2CPP APK	4.1
IL2CPP IPA	2.25

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