Improve documentation for property plugin.bitbucket-git.author.name.type

Issue Summary

The current documentation for property plugin.bitbucket-git.author.name.type states that the property will change how the committer author will be shown, but this only affects Git logs and doesn't affect Bitbucket UI.

Steps to Reproduce

1. Add the property on bitbucket.properties set to "username"
2. Restart Bitbucket
3. Commit and push a change via Bitbucket UI
4. Check the git log to see that it now will show the Bitbucket username instead of the display name.

Expected Results

Please adjust the documentation for a better understatement of the feature. For example, specify that this feature only affects how the author will be shown in the logs.

Actual Results

N/A

Workaround

Explain to the customer that this is specifically related to how git will show the author name when a commit is made via Bitbucket UI.