Refactor LfsRequest to stop referencing auth::result.actor directly

What does this MR do?

in #328692 there were remarks regarding how we handle find_for_git_client method results. This method is returning Gitlab::Auth::Result instance.

In Gitlab::Auth::Result as an actor we can have DeployToken or User, which is causing confusion and may lead to some problems: https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/1356.

My goal here is to create more resilient and less confusing code.

Goal 1: stop using .actor with checking the type.

Here I implemented changes in LFS facing endpoints: they no longer using user derived from actor from Gitlab::Auth::Result class, but separately DeployToken instance or User instance.

In LfsApiController and LfsStorageController we do not call user directly - authorization goes through LfsRequest module

In LfsLocksApiController we need User instance - looking at what is implemented in the services.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

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.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team