Time and query limits

[simonw]

Refs #33. Still needs:

• [x] Configuration
• [x] Tests
• [x] Documentation

[simonw]

Two configuration options:

• total time allowed for queries during a single GraphQL execution
• total number of table SQL queries allowed during a single GraphQL execution

[simonw]

plugins:
  datasette-graphql:
    time_limit_ms: 2000
    num_queries_limit: 200

[simonw]

Setting these to 0 should disable the limits.