[develop2] Test lockfiles conan lock add pkg/version#revision when existing revisions

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The manually added revision will in general not have a timestamp, but it is required for doing the right insertion and ordering.
Would we want to make it the "latest" by default when manually adding? Should it error if timestamp not present?

Note that it won't be an error if other revisions don't exist, as locking it is trivial.

Comes from the Tribe discussion conan-io/tribe#34 (comment) from @mec-irobot

[memsharded]

Closed by #11184