Refactor and cleanup CLI module

[juhoinkinen]

Changes:

• Move the helper functions & decorators to a new cli_util.py module (as commented in https://github.com/NatLibFi/Annif/pull/663#discussion_r1095437426)
• Use dict instead of collections.OrderedDict
• Make docs-limit option a common decorator
• Add a few docstrings to helper functions
• Cosmetic fix for unnecessarily split strings
• Mark internal helper functions of cli_util.py as private with underscore
• Simplify helper function to set the project config file path

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov[bot]]

Codecov Report

Base: 99.56% // Head: 99.56% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (d1a5043) compared to base (3e8f42f). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #675 +/- ## ======================================= Coverage 99.56% 99.56% ======================================= Files 87 88 +1 Lines 6158 6171 +13 ======================================= + Hits 6131 6144 +13 Misses 27 27 ``` | [Impacted Files](https://codecov.io/gh/NatLibFi/Annif/pull/675?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi) | Coverage Δ | | |---|---|---| | [annif/cli.py](https://codecov.io/gh/NatLibFi/Annif/pull/675?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi#diff-YW5uaWYvY2xpLnB5) | `99.62% <100.00%> (-0.08%)` | :arrow_down: | | [annif/cli\_util.py](https://codecov.io/gh/NatLibFi/Annif/pull/675?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi#diff-YW5uaWYvY2xpX3V0aWwucHk=) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi)

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