[#82] Pretty `ToJSON` instances

[DK318]

Description

Problem

At this moment ToJSON instances leak a lot of internal info. Some of them look very ugly (e.g. EntryPath).

Solution

Used deriveToJSON (aesonPrefix camelCase) to derive some instances. QualifiedPath ToJSON instance is handcrafted. Also removed unnecessary FromJSON instances.

Related issue(s)

• Fixes #82

Fixed #

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Related changes (conditional)

• Tests

  • [ ] If I added new functionality, I added tests covering it.
  • [ ] If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • [x] I checked whether I should update the docs and did so if necessary:
  • README
  • Haddock

Stylistic guide (mandatory)

• [x] My commits comply with the policy used in Serokell.
• [x] My code complies with the style guide.