Recover from vuln DB download failure using cached DB

**Motivation**
For our vulnerability scanning flow, cloudbeat will use Trivy to scan the available AWS account volumes. Cloudbeat starts every cycle with downloading the vulnerabilities DB, when it fails the whole flow fails. Instead, cloudbeat can hold in cache the vulnerabilities DB from the prior cycle and if a download fails it can continue with the flow by using the cached DB.

**Definition of done**
- [ ] Cloudbeat should instruct trivy to read the vulnerabilities database from the downloaded file
- [ ] A failed database download should try to use the cached DB
- [ ] When using the cached DB cloudbeat health should be degraded

**Related tasks/epics**
- https://github.com/elastic/cloudbeat/issues/697