CLOUDP-236398: Adding merge command skeleton

[andreaangiolillo]

Proposed changes

Jira ticket: CLOUDP-236398

./bin/openapicli merge --help                       
Merge Open API specifications into a base spec.

Usage:
  openapicli merge -b [base-spec] -e [spec-1] -e [spec-2] [flags]

Flags:
  -b, --base string            Base OAS. The command will merge other OASes into it.
  -e, --external stringArray   OASes that will be merged into the base OAS.
  -h, --help                   help for merge
  -o, --output string          File name where the command will store the output. (default "FOAS.json")

./bin/openapicli merge -b test.json -e external.json
2024/03/08 15:29:51
Merged spec was saved in 'FOAS.json'

Checklist

• I have signed the MongoDB CLA
• I have added tests that prove my fix is effective or that my feature works

Further comments