Currently all API requests set Cache-control: no-cache to avoid browsers
caching sensitive data. This fixes so that all responses returned from
backend not are cached using http headers. The exception is the data proxy
where we don't add these http headers in case datasource backend needs
to control whether data can be cached or not.
Fixes#16845
This changes forks the mysql part of the Macaron session middleware.
In the forked mysql file:
- takes in a config setting for SetConnMaxLifetime (this solves wait_timeout
problem if it is set to a shorter interval than wait_timeout)
- removes the panic when an error is returned in the Exist function.
- retries the exist query once
- retries the GC query once
