Filter gitlab objects with functions

[iamrgroot]

I think it would be really nice to remove the settings for skipping item states and replace them with filter functions.

Now:

 skipMergeRequestStates: string[];
 skipMatchingComments: string[];

Suggested:

 skipIssue: (issue: GitLabIssue) => boolean;
 skipMergeRequest: (mr: GitLabMergeRequest) => boolean;
 skipNotes: (note: GitLabNote) => boolean;
 skipMilestone: (note: GitLabMilestone) => boolean;

An example config could be:

 skipMergeRequest: (mr: GitLabMergeRequest) => ['merged', 'closed'].includes(mr.state),
 skipIssue: (issue: GitLabIssue) => {
 if (!issue.closed_at) {
 return false;
 }

 return (new Date(issue.closed_at)).getFullYear() < 2023;
 },