* fix: make bank_id metric label opt-in to prevent OTel memory leak
bank_id as an OTel metric attribute creates unbounded histogram growth
since each unique bank_id produces never-evicted time series. Default
to excluding it; opt in with HINDSIGHT_API_METRICS_INCLUDE_BANK_ID=true
for deployments with few banks.
Closes#850
* refactor: use config.py for metrics_include_bank_id setting
Move HINDSIGHT_API_METRICS_INCLUDE_BANK_ID from direct os.getenv in
metrics.py to the standard HindsightConfig path. Add configuration
documentation.
cf4bd598b4