Shared JSON spec for span types/subtypes

[SylvainJuge]

Description

Creates and enforces JSON spec for all the span types/subtypes that are used in the Java agent

This is a preliminary step to having a shared spec applied to all APM agents.

Related PR for all agents : elastic/apm#443

Checklist

• gather the list of all values currently reported by tests for the Java agent to make test pass.
• decide how to handle values for test only
  • sharing those across agent does not make sense
  • applying a wildcard or prefix-based approach hardcoded before the check could help (for example do not validate every foo.* type.
  • Solution: Allow manual opt-out on a per-test-method basis
• decide how to handle null (not provided) or "" (empty) sub-types:
  • should we make them optional on some known types ? making them optional on every type ?
  • Solution (1): normalize to null instead of empty and treat sub-type as optional
  • Solution (2): normalize to null instead of empty and allow null on some types (not all of them).
• decide how to handle "open ended" span subtypes:
  • process type that uses binary name as sub-type (or find a proper way to fix it).
  • Solution: remove subtype that was using binary name, it's already provided in name
  • template type that uses template engine name as sub-type (and is also very platform-specific)
  • Solution: enforce only the type and not subtype as it's really platform-specific
• decide what to do with OpenTracing & OpenTelemetry bridges
  • remap cache.redis to db.redis for consistency
  • use custom as default span type instead of unknown

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Build stats

• Build Cause: Pull request #1812 updated

• Start Time: 2021-06-02T13:21:59.807+0000

• Duration: 51 min 12 sec

• Commit: 7c27ff3

Test stats 🧪

Test	Results
Failed	0
Passed	2189
Skipped	18
Total	2207

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Test stats 🧪

Test	Results
Failed	0
Passed	2189
Skipped	18
Total	2207

[SylvainJuge]

See elastic/apm#443 PR for adding this to shared specifications.

[eyalkoren]

LGTM, few minor comments and one question about the spec itself - for a given type, is null subtype allowed when the spec defines a list of subtypes?

[eyalkoren]

❤️

[eyalkoren]

LGTM! One minor suggestion