Exclude `/metrics` from OpenAPI schema by default & allow to configure the exclusion

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Flag	Coverage Δ
unittests	97.89% <100.00%> (+<0.01%)	:arrow_up:

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Files with missing lines	Coverage Δ
microbootstrap/bootstrappers/fastapi.py	96.77% <ø> (ø)
microbootstrap/bootstrappers/litestar.py	97.05% <ø> (+0.04%)	:arrow_up:
...icrobootstrap/instruments/prometheus_instrument.py	100.00% <100.00%> (ø)

[vrslev]

Let's grab that parameter from settings, cause someone might need it

Done. I didn't add tests: they'd be to fragile and messy