[#9] Directory check in `create` command

[DK318]

Problem: we can create entries and directories with the same names. Solution: added subfunction checkForEntriesInEntryPath which tries to find an existing entry subpath in given path. Then checked if the given entry path is an existing directory or contains existing entries in subpaths.

Description

Related issue(s)

• Fixed #9

  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

  • Public contracts

    • [x] Any modifications of public contracts comply with the Evolution of Public Contracts policy.
    • [x] I added an entry to the changelog if my changes are visible to the users and
    • [x] provided a migration guide for breaking changes if possible

  Stylistic guide (mandatory)

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

[dcastro]

Please tick off items from the PR checklist as appropriate.

The Public contracts section doesn't really apply at the moment, because we haven't released anything yet, so you can tick those off too.

[dcastro]

And add the issue number in the "related issues" section, e.g. Fixed #9. When a PR has this in its description, github will automatically close the issues when the PR is merged.