Classify EE trial feature as SaaS or SM

What does this MR do?

Mark files or code sections with a comment marker, indicating whether that's for SaaS or self manged instance.

Often I need to study part of the code to know if it is for SaaS or self managed. This MR will save this time when ever I revisit this part of the code base, and not mistaken SaaS with SM code.

This MR focus on trial related code.

See #338034 for more discussions.

Does this MR meet the acceptance criteria?

Conformity

• [-] I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.