Make --output flag support all types of paths

[mosmartin]

What was the problem?

This PR resolves #9090

How was it solved?

Created the handleOutputFlag utility function.
With this utiliy, it's now possible to generate output files with following commands

1. ./bin/run generator export will generate a file with the default namespace name in the cwd.
2. ./bin/run generator export --output . will generate a file with the default namespace name in the cwd.
3. ./bin/run generator export --output ./ will generate a file with the default namespace name in the cwd.
4. ./bin/run generator export --output test.json will generate the file with the provided filename in the cwd.
5. ./bin/run generator export --output ~ will generate a file with the default namespace name in the user home dir.
6. ./bin/run generator export --output ~/Desktop/ will generate a file with the default namespace name in the user desktop.
7. ./bin/run generator export --output exports will generate a file with the default namespace name in the defined dir (exports) in cwd
8. ./bin/run generator export --output /Users/johndoe/Public/test.json will generate the test.json file in the defined path

How was it tested?

Updated and added new tests

[codecov]

Codecov Report

Merging #9169 (f92b2c5) into release/6.1.0 (f641009) will decrease coverage by 0.01%.
The diff coverage is 93.22%.

❗ Current head f92b2c5 differs from pull request most recent head 4500f0b. Consider uploading reports for the commit 4500f0b to get more accurate results

Additional details and impacted files

@@                Coverage Diff                @@
##           release/6.1.0    #9169      +/-   ##
=================================================
- Coverage          84.65%   84.65%   -0.01%     
=================================================
  Files                655      656       +1     
  Lines              24113    24122       +9     
  Branches            3497     3497              
=================================================
+ Hits               20414    20420       +6     
- Misses              3699     3702       +3     

Files	Coverage Δ
...der/src/bootstrapping/commands/generator/export.ts	91.30% <100.00%> (-1.29%)	⬇️
commander/src/bootstrapping/commands/hash-onion.ts	82.75% <100.00%> (-3.36%)	⬇️
...ommander/src/bootstrapping/commands/keys/create.ts	100.00% <100.00%> (ø)
...ommander/src/bootstrapping/commands/keys/export.ts	94.73% <100.00%> (-0.51%)	⬇️
...er/src/bootstrapping/commands/passphrase/create.ts	100.00% <100.00%> (ø)
...r/src/bootstrapping/commands/passphrase/encrypt.ts	100.00% <100.00%> (ø)
commander/src/utils/flags.ts	100.00% <ø> (ø)
commander/src/utils/output.ts	100.00% <100.00%> (ø)
...mander/src/bootstrapping/commands/config/create.ts	34.28% <20.00%> (-2.08%)	⬇️

... and 1 file with indirect coverage changes