[rush] rush update --full reported beta version as available major upgrade

[jeremymeng]

Summary

In our repo we check available major version upgrades using the following steps

For some package, the available major version upgrades only had beta releases, no stable versions yet. Maybe it's better to not report them as available major upgrades until a stable version has been released?

For example, when the above issue was logged, fast-xml-parser 4.0.0 stable version hadn't been published.

Expected result:
available major upgrades that only have beta releases so far are not reported

Actual result:

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
@microsoft/rush globally installed version?	5.55.1
rushVersion from rush.json?	5.55.1
useWorkspaces from rush.json?	not using this option
Operating system?	All
Would you consider contributing a PR?	No
Node.js version (node -v)?	14.15.1

[iclanton]

Related to #3169, this isn't a Rush feature. Rather, this is implemented by some packages' postInstall scripts and by some package managers.