[Feature] Add env for query retry

[surgachsurgach]

prequisite: getredash/redash#5791

[grugnog]

@surgachsurgach thanks for this!
We actually source environment variables from https://github.com/getredash/website/blob/master/src/pages/kb/open-source/admin-guide/env-vars-settings.md via a helper script - this helps ensure we aren't straying from what is documented upstream.
Would you be able to add an issue and/or PR to https://github.com/getredash/website/ to document this env var? It seems like this repo is only tended to occasionally, so if you don't want to wait for that to be merged also we could add a chunk to the script to add this in the mean time (like we did for SAML_SCHEME_OVERRIDE) referencing the upstream issue.

[grugnog]

Closing this until upstream is merged