Added an 'author' argument for the DiffChangelogCommand

[EggOxygen]

This PR introduces an 'author' argument to support the diff-changelog command in liquibase/liquibase#3990.

I tested it on a Gradle-based project and ran diffChangelog. The changesets' author appears to be functioning correctly with the one I provided.

[MalloD12]

Approved.

Review and testing results:

Code looks good to me. I could also see author is being set correctly in the generated changelog.

Things to be aware of:

• None

Things to worry about:

• None

[stevesaliman]

I added the author argument to GenerateChangeLogCommand since that command also supports it in Liquibase.

I also updated the changelog, changed the version to a SNAPSHOT version, and made the order of constants more consistent with the others.

[unlimitedsola]

Thanks to everyone who worked on this! Can we get a new version released for this?

We have a custom Gradle setup where we wanted to use the contributor's Git username as the author to generate changelogs and we're excited about this to be fixed.

[MalloD12]

cc: @stevesaliman ^^

[stevesaliman]

I had some other things I had hoped to fix in the next release, but I'm not sure if I'll be able to. I can do a release for this fix over the weekend.

[unlimitedsola]

@stevesaliman Sorry for bothering you again, is there anything that we can help with to get a new version released?

[stevesaliman]

Version 2.2.1 was released this morning. Sorry for the delay.

[unlimitedsola]

❤️ Thanks for your hard work!