Refactor Page::Component invite member modal actions

What does this MR do?

Addressing flakiness with invite member modal #336305 (comment 630404621) .

• Re-organized the steps under add_member via UI: select the user first before selecting the access level.
• Fixed access level selection, passing in access level value no longer works, replaced value with actual text name.
• Since 'Guest' option is selected by default on the form, skipping this step if desired option is 'Guest'
• Also update tests that use this logic.

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.

Related to #336305 (closed)