BUGFIX: Add exponential backoff when reading from Redis

[kdambekalns]

When Redis is not ready (yet) when trying to read from the cache, this makes Flow wait and retry up to 8 times with an exponentially growing back-off time.

Fixes #3284

Review instructions

This might be hard to check in real life, sorry…

Checklist

• [x] Code follows the PSR-2 coding style
• [ ] Tests have been created, run and adjusted as needed
• [x] The PR is created against the lowest maintained branch
• [x] Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• [ ] Reviewer - The first section explains the change briefly for change-logs
• [ ] Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions