Add JF_MSI env var

[orz25]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.

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Analyzer Manager is expecting to get the multi_scan_id as env variable named JF_MSI. Added this variable right after we get the multi_scan_id from xsc.

PR in jfrog-cli-security using this branch as jfrog-client-go package (for test purposes):
jfrog/jfrog-cli-security#5

[github-actions]

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🐸 JFrog Frogbot

[eyalbe4]

Before we can merge this PR, you should go ahead and create two additional PRs for the jfrog-cli-core and jfrog-cli projects, so that we can see that the tests that those projects include, and may be impacted by this change, as passing.
You'll need to use the replace statements in the go.mod files of those projects, to reference this PR's branch (your fork) for both of your jfrog-client-go and jfrog-cli-core. It'll be helpfull if you link all of the 3 PRs by adding referencing them in the descriptions of the PRs.

[eyalbe4]

The above code can be simplified as follows. In addition, the error created should be wrapped with errorutils.CheckErrorf(err) iin this case, beucase os.Setenv, which may return the error, is an external API to the jfrog-client-go codebase. Also notice that in the above code the original error is lost, and the below code fixes that as well.

if err = os.Setenv("JF_MSI", multiScanId); err != nil {
	errorutils.CheckErrorf("failed setting msi as environment variable. Cause: %s", err.Error())
}