Update vault flags loading

[Zhaars]

Used network.NewTLSConfigByName method for loading TLS config from cli. Flags. Added missing flag registration for acra-backup

Checklist

• [ ] Change is covered by automated tests
• [ ] The coding guidelines are followed
• [ ] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [ ] CHANGELOG.md is updated (in case of notable or breaking changes)
• [ ] CHANGELOG_DEV.md is updated
• [ ] Benchmark results are attached (if applicable)
• are up-to-date (in case of API changes)