Enhancements to Release Bundle Create Command.

[oshratZairi]

• All tests have passed. If this feature is not already covered by the tests, new tests have been added.
• 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 ./....

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Enhanced behavior of the release bundle create command:

1. The spec flag is now optional, with the build-name and build-number flags serving as replacements.
2. Support has been added for the JFROG_CLI_BUILD_NAME and JFROG_CLI_BUILD_NUMBER environment variables as fallback options when the build-name and build-number flags are omitted.

documentation: jfrog/documentation#173