Improve output of outdated dependency command

In the discussion linked below, we came up with an improvement to the output of the gleam deps outdated command.

We would have 1 line stating how many outdated packages were found, a new line and then the table (if outdated packges > 0). For example:

$ gleam deps outdated
1 out of 12 packages have newer versions available.

Package       Current  Latest
-------       -------  ------
gleam_stdlib  0.70.0   0.71.0

$ gleam deps outdated
0 out of 12 packages have newer versions available.

The goal of this design is for the case of no outdated dependencies to not be silent (no output), while for other tools, that rely on this command, to still output something that is parsable in an easy manner.

Reference discussion: https://github.com/gleam-lang/gleam/discussions/5484

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Edit: use '# of # packages have newer versions available' for the message