apollo_dashboard: extract shared exchange-rate oracle alert builders (#14702)

[matanl-starkware]

Backport of #14702 to main-v0.14.3.

Clean git cherry-pick -x of f4c4a022f5. No starknet_version change (V0_14_3 preserved).

[reviewable-StarkWare]

This change is 

[cursor]

PR Summary

Low Risk
Alert-only refactor in apollo_dashboard with behavior preserved; no runtime or gas-price logic changes.

Overview
Moves ETH→STRK Grafana alert definitions out of alert_definitions.rs into l1_gas_prices.rs and factors shared Prometheus logic into oracle_success_count_alert and oracle_error_count_alert.

get_eth_to_strk_success_count_alert now delegates to the success helper (still sum_increase over 1h, fires when < 1 success). get_eth_to_strk_error_count_alert is re-exported from the L1 gas prices module and built via the error helper: sum_increase over 1h with or vector(0) so missing series do not cause no-data, threshold > 10 errors, 1m pending, Informational severity—matching the prior inline definition.

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