[api] Make the limit on spending power on the retire API configurable per team

[biwano]

Users of the retirement API can decide on a limit on spending power per week in the limit of 5000 USDC per key.
We want to add a limit on the overall spending power of a team controlled by Carbonmark.

Describe the solution you'd like

• Add a limit_cost_usdc_per_week in the team database with a default value of 5000
• Add a trigger that prevent modifying this value by non admins.
• Add a check in the retire endpoint that checks:
  Total spent by all the keys during the last week + Cost of the new trasaction < team.limit_cost_usdc_per_week