[ML] Update wording during upload file wizard with "Next"

[nicpenning]

Describe the feature:
As a user, I found it confusing when I uploaded a file and the next step was to "Import" and I still wanted to tweak more settings. After I realized there was nothing more to do I hit Import and was taken to the next phase of the file upload process where more customizations can be made.

I recommend that this simply be changed to "Next" so the user can expect there is more work to do and they will not be importing when they click that button.

Describe a specific use case for the feature:
Make it easier to upload a file and configure without any hesitation.

Recording.2023-06-15.110900.mp4

[mbondyra]

@elastic/kibana-gis not sure if this belongs to you (I followed CODEOWNERS file), feel free to redirect if not

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[jsanz]

@elastic/ml-ui could you please take a look at this and #159829 ?

[nicpenning]

Any updates here?

[peteharverson]

@jgowdyelastic I've added the 8.16.0 label to this one so that we can look to see if there is anything we can do here as part of upcoming enhancements to the file upload UX.