feat: token bucket rate limiting

[craigzour]

Summary | Résumé

Should not be merged until V1 is released to production (unless we decide to include it in V1).

Context: cds-snc/platform-forms-client#3947

• Implements token bucket rate limiter using two different bucket capacities
  • Low rate limit is 500 requests per minute
  • High rate limit is 1000 requests per minute
• Renames and moves cache (in lib/utils) to redisClientAdapter (in lib/integration/redis). The rate limiter code uses Redis to get a value that will be set by the web application. Since there is no cache concept involved here I decided to rename the two cache related functions. This way we can use it everywhere we need to access Redis and it also simplifies the mocks in our unit tests.

Test instructions

• Modify the config.ts file to lower the token bucket capacity for both lowRateLimiterConfiguration and highRateLimiterConfiguration
• Send request to the API and observe both the response headers (there should be some new X-RateLimit properties) and response HTTP code (will be 429 when you have reached the limit)
• If you want to enable the high capacity bucket token just add a new entry in Redis with the following key/value pair: rate-limit:${formId} => "high"

[craigzour]

A maximum of 500 requests per minute is going to be what we ask our prototyping partners to follow for V1. When the Rate limiter is released we will actually be able to see whether it is a good starting point for our users.

[craigzour]

The high capacity token bucket is not going to be used for now as the web app feature to enable it is not a priority at the moment.