Add dump path check

[FabijanC]

Usage related changes

• Check if the directory of the dump paths exists (when specified through CLI and through HTTP).

Development related changes

• Alphabetically sort imports in some files.
• Change dump tests to explicitly check for status code == 1
• Change order of set_dump_options and generate_accounts so that failure in case of an invalid dump path happens sooner.

Checklist:

• No linter errors
• Performed a self-review of the code
• Rebased to the last commit of the target branch (or merged it into my branch)
• Documented the changes
• Updated the tests
• All tests are passing