Add CLI for fetching sp promotions

[michaeldjeffrey]

Fetch from mobile-config the same way they as the rewarder does. Print them in a nice little list.

Running with no options defaults to Utc::now().

>>> ./mobile-verifier -c ../../mobile-verifier.toml service-provider-promotions 

Service Provider: HeliumMobile
  incentive_escrow_bps: 396
  Promotions: (1)
    name: Referral Elite
    duration: 1year 2months 1day 20h 52m 48s (2024-10-29T00:00:00Z -> 2025-12-31T00:00:00Z)
    shares: 100

Passing the --start option.

>>> ./mobile-verifier -c ../../mobile-verifier.toml service-provider-promotions --start "2024-10-30T00:00:00Z"
Promotions as of 2024-10-30 00:00:00 UTC
Service Provider: HeliumMobile
  incentive_escrow_bps: 396
  Promotions: (1)
    name: Referral Elite
    duration: 1year 2months 1day 20h 52m 48s (2024-10-29T00:00:00Z -> 2025-12-31T00:00:00Z)
    shares: 100

>>> ./mobile-verifier -c ../../mobile-verifier.toml service-provider-promotions --start "2024-10-29T01:00:00Z"
Promotions as of 2024-10-29 01:00:00 UTC
Service Provider: HeliumMobile
  incentive_escrow_bps: 396
  Promotions: (1)
    name: Referral Elite
    duration: 1year 2months 1day 20h 52m 48s (2024-10-29T00:00:00Z -> 2025-12-31T00:00:00Z)
    shares: 100