Allow to use many location in dbpopulator

[mkuziemko]

Description

Changes proposed in this pull request:

• add support for using many locations in dbpopoluator

This change required code refactoring:

• the logic of checking if there is a need to populate manifests was transferred to new methods,
• there is running one server for serving JSON files. Due to that, there was a need for a new structure.

Additionally, I added a todos which need further work in the future.

As always, comments or suggestions are appreciated.

Related issue(s)

• https://github.com/capactio/capact/issues/560

[mszostok]

Before merging, please prepare follow-up PRs for all repos where populator is used, so after merging new version we can easily reduce “downtime”.

For example, after merging this PR, new populator will be released and this PR https://github.com/capactio/hub-manifests/pull/51#pullrequestreview-860576961 on hub-manifests will be not properly validated