Allow to specify git tag message

[aguschin]

Right now a message that is generated for created git tags follows the same format. User may want to specify that one to reflect some details about version registration or promotion. Something like this should work:

$ gto register rf -m "My message"

[aguschin]

As mentioned by @amritghimire, the commit message should also appear in check-ref. And maybe in history and show mymodel?

[aguschin]

Then I think check-ref by default should print something human-readable, and the current output should be presented with --json only.

[Suor]

@amritghimire said to me that tag message is missing from .check_ref() not the commit one.

[amritghimire]

Commit message is also missing there, but it was possible to extract commit message in our use case. The requirement was having tag message.