Adding PEM certificate troubleshooting

[anaxceron]

Describe your pull request here: Adding Zowe CLI troubleshooting content for PEM certificates

List the file(s) included in this PR: troubleshoot-cli-credentials.md

After creating the PR, follow the instructions in the comments.

[github-actions]

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[github-actions]

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[gejohnston]

I suggested a couple of small possible additions.
I will am willing to defer to team consensus on whether or not to include those suggestions.

[zFernand0]

Thank you for addressing the comments 😋
LGTM! 😋

[sbohnert]

Looks good, Ana. Thanks