feat(integration): Raise BadGatewayError on 502 errors

[julienbourdeau]

If Anrok returns a Bad Gateway error with a 200 status, we handle this by raising a custom Integrations::Aggregator::BadGatewayError. See #3234

This error can be use to retry the job, like for RefreshOngoingBalanceJob

lago-api/app/jobs/wallets/refresh_ongoing_balance_job.rb

Line 11 in b1596cd

retry_on Net::ReadTimeout, Integrations::Aggregator::BadGatewayError, wait: :polynomially_longer, attempts: 6

Unfortunately, of the error is a return with a 502 status, we'll raise a regular LagoHttpClient::HttpError, which is not retrie

This PR aligns the behavior to always raise this custom error.

Notice that this custom error extends the HttpError:

lago-api/app/services/integrations/aggregator/bad_gateway_error.rb

Line 5 in b1596cd

class BadGatewayError < LagoHttpClient::HttpError

Main changes

1. refactor tests to use webmock instead of mocking the client
2. rename BAD_REQUEST_ERROR to BAD_GATEWAY_ERROR
3. make bad_gateway_error?(e) return true if status is 502 (not just content grepping)
4. raise BadGatewayError instead of HttpError