Create factory methods in all API classes

[Art4]

Affected classes:

• Redmine\Api\Attachment
• Redmine\Api\CustomField
• Redmine\Api\Group
• Redmine\Api\Issue
• Redmine\Api\IssueCategory
• Redmine\Api\IssuePriority
• Redmine\Api\IssueRelation
• Redmine\Api\IssueStatus
• Redmine\Api\Membership
• Redmine\Api\News
• Redmine\Api\Project
• Redmine\Api\Query
• Redmine\Api\Role
• Redmine\Api\Search
• Redmine\Api\TimeEntry
• Redmine\Api\TimeEntryActivity
• Redmine\Api\Tracker
• Redmine\Api\User
• Redmine\Api\Version
• Redmine\Api\Wiki

Closes #368

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.65%. Comparing base (63b0368) to head (269a996).

Additional details and impacted files

@@             Coverage Diff              @@
##               v2.x     #458      +/-   ##
============================================
+ Coverage     98.52%   98.65%   +0.12%     
- Complexity      661      721      +60     
============================================
  Files            29       29              
  Lines          2033     2153     +120     
============================================
+ Hits           2003     2124     +121     
+ Misses           30       29       -1     

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