WIP: Add general `CI` and integration with `mean`

[smishr]

EDIT: 26.02.23 Remaining to do on this PR. Integration with other summary functions (total etc) can be done in separate PR's. See their issues

• [ ] Add doctests
• [ ] Review code formulae with theory/textbook

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Doing #184

Currently testing integration with mean.

Finding way to integrate with least amount of changes in existing API.

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (v0.1.1@4fac910). Click here to learn what that means. The diff coverage is n/a.

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[smishr]

@ayushpatnaikgit please see how i integrated confidence intervals into mean.jl now

[smishr]

@itsdebartha you may continue this PR, just like mean, add CI functionalities for total quantile and ratio in their respective files