If project flag provided with empty value, act like there is no project

[yahavi]

• The pull request is targeting the dev branch.
• The code has been validated to compile successfully by running go vet ./....
• The code has been formatted properly using go fmt ./....
• All static analysis checks passed.
• All tests have passed. If this feature is not already covered by the tests, new tests have been added.

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Flags always have priority over environment variables. However, if the JFROG_CLI_BUILD_PROJECT environment variable is set to --project='', it's considered as the project being provided.

[attiasas]

LGTM