Update request_end instrumentation example

[bdewater]

The old example would send IDs (high cardinality - which can be expensive) for URLs like /v1/accounts/acct_123/persons. The new example tries to filter out anything that looks like an ID, it support nested/namespaced examples such as /v1/financial_connections/accounts/:id/disconnect or endpoints with multiple IDs such as /v1/transfers/:id/reversals/:id.