[#44] Merge `--filter` and `--filter-field` options

[sancho20021]

Description

Problem

@Heimdell in #44 suggested to merge --filter and --filter-field options into a single --filter option.

e.g.:

--filter name~vault               <- filter entries by entry name
--filter url:value~google.com     <- filter entries by field value

Solution

Modified parseFilter :: MParser Filter supplementing it with parseFilterByField's functionality.

Changed related datatypes so there is no separation between filter and filter-field.

Related issue(s)

• Fixed part of #44:
  • [x] core has filters merged
  • [x] CLI has filters merged

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Related changes (conditional)

• Tests

  • [x] If I added new functionality, I added tests covering it.
  • [x] 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

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