Support external Postgresql database server

[azhelev]

Description of the change

Adds support for using external Postgresql server

Type of change

• [ ] Bug fix (non-breaking change that fixes an issue)
• [x] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Related issues

Checklists

Development

• [ ] Lint rules pass locally
• [ ] The code changed/added as part of this pull request has been covered with tests
• [ ] All tests related to the changed code pass in development

Code review

• [ ] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• [ ] "Ready for review" label attached to the PR and reviewers mentioned in a comment
• [ ] Changes have been reviewed by at least one other engineer
• [ ] Issue from task tracker has a link to this pull request

[politician]

@lokey Can someone please take a look at this PR?

[nauxliu]

Will there be a problem if multiple workers share one Postgresql instance? as far as I know every worker has its own Postgresql.

[ldaugusto]

Will there be a problem if multiple workers share one Postgresql instance? as far as I know every worker has its own Postgresql.

That's a good point. If a single db instance can handle multiple servers, why does the chart load a new postgres for every server instance.

[gitcommitshow]

@azhelev can you please check the comments in this PR

[gitcommitshow]

As shared by @psrikanth88, this PR has some unaddressed comments. And it would work with only one replica of statefulset. If there are multiple, it needs extra configuration support in our code to use different schema in same external postgres for each replica.

[azhelev]

I don't use this anymore, i have no interest in completing this PR. If someone wants to take it up feel free.