Show default sampling strategy with per-operation sampling

[yurishkuro]

Short description of the changes

• adds per-operation strategies to the default_strategy section of the sample configuration
• reflects changes in PR Make operation_strategies part also be part of default_strategy  jaeger#1749 (ticket Allow default per-operation sampling strategies jaeger#1748)

[rutgerbrf]

Looks good! Perhaps it should be noted that the default sampling probability is 0.1%, if no default strategy is configured (or maybe not, because of architecture.md, though that is about the client).

[yurishkuro]

@rutgerbrf thanks for review, added a note about default prob.