feat(level): Support current as the maximum level

[zFernand0]

When dealing with prereleases, we may want to lock down the labels to only allow release-current.
In that case, we should probably introduce the level: current to the list of accepted level definitions in a protected branch.
Source: https://github.com/zowe-actions/octorelease/blob/master/packages/core/src/doc/IProtectedBranch.ts#L34

Otherwise, we could assume that if prerelease != null && prerelease !== false (or simply if(prerelease)) then we always do current without asking for labels.

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Notes:

• We should ideally support the ability to assign major, minor, and patch for prereleases 😋
• The following PR contains an example of how this could be tested
  • Remove the 'zowe profiles' command group zowe/zowe-cli#2013