[telemetry] Split user tables: local (MAU), CI/CD, and agent, plus a combined total

[hemarina]

Problem

MAU today counts local/desktop users only. CI/CD and agent traffic is excluded, even though it is a large share of overall usage. As a result:

• We cannot report a total user number.
• We cannot see users transitioning from local to CI/CD, which is a success signal, not attrition.
• Agent usage is growing and is invisible in our headline metrics.

What we'll do

Build separate tables so each surface can be reported on its own, plus a combined view:

1. Local users (MAU)
2. CI/CD
3. Agent
4. Combined — all three added together for a total user count

These should be driven by execution.environment, which azd already emits.

Known classification bugs to fix as part of this

• cli/azd/internal/tracing/resource/exec_environment.go joins modifiers onto the base value with ; (for example Azure Pipelines;Azure App Spaces Portal), but the Kusto side matches values exactly, so any modified value falls through the classification.
• GitHub Copilot App is defined in fields.go but is missing from the Kusto environment lists, so those users are misclassified.

Classification should be defined in one place so adding a new environment value is a single change.

Done when

• Four tables exist and agree with each other.
• Every value azd emits is classified, including modified values.
• Adding a new environment value is a one-place change.