Move validation logic from Vue component to resolvers

What does this MR do?

In preparation of moving table to GlTable as a part of #267953 (closed) we are removing row related logic and move it in proper place. Previously we were triggering validations on component side, now we mimic typical behavior of store-based applications - trigger validation when we are performing mutation

Basically, no changes visible to end-user are made as a part of this MR

Screenshots or Screencasts (strongly suggested)

GitLab__2_

How to setup and validate locally (strongly suggested)

• Enable feature bulk_import via Feature.enable(:bulk_import)
• Open "New group" (/groups/new)
• Use https://gitlab.com as source instance and GeK1Nis4j-SY1X4sqE5c as personal access token (this token is from separate user on GitLab instance with 0 real data available, so we do not expose any security risks here)
• Modify any dropdown to target existing project (note: right now this is case sensitive, it is known issue and out of scope of this MR) lete any tasks that are not applicable. -->

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
  • Changelog is not needed, feature is behind feature flag
• 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.