GitLab: Skip author filtering when group or project tokens are in use

[rarkins]

Describe the proposed change(s).

Migrate ignorePrAuthor to platformAuthorFilter. Default value should be auto and with possible options auto, enabled, disabled.

For GitLab, when platformAuthorFilter=auto then it should set that to disabled if the bot username starts with group_ or project_. i.e. download all Issues and MRs if such a token is in use.

Otherwise platformAuthorFilter=auto should default to enabled, including for other GitLab token types plus other platforms. i.e. retain same behavior as today.

Migrate:

• ignorePrAuthor=true to platformAuthorFilter=disabled
• (explicitly configured) ignorePrAuthor=false to platformAuthorFilter=enabled