[upload] The behavior of -force-overwrite is ambiguous

[nanjiangshu]

Describe the bug
When the flag -force-overwrite is set, for example

sda-cli -config s3cmd.conf upload --force-overwrite  -encrypt-with-key c4gh.pub.pem t1.txt

The command will exit with an error:

Skipping input file t1.txt. Reason: outfile t1.txt.c4gh already exists. 

One would expect it overwrites both the local encrypted file and force uploads the file to the inbox.

Steps to reproduce

Expected behavior

• The behavior of -force-overwrite should be clear and more intuitive.
• Tests verifying the fix are added

Additional context

Estimation of size: small/medium/big

Estimation of priority: low/medium/high