Replace loading icon (spinner) size md with lg

What does this MR do and why?

Partly solves #29847 (closed)

*There are currently ~77 instances of size="md" - it will be cleaner/easier to take this in steps.

Screenshots or screen recordings

number	md	lg
1
2

How to set up and validate locally

number	file	steps
1	app/assets/javascripts/access_tokens/components/projects_token_selector.vue	Enable the personal_access_tokens_scoped_to_projects feature flag. Navigate to /-/profile/personal_access_tokens
2	app/assets/javascripts/clusters_list/components/clusters_view_all.vue	Navigate to <ORG>/<GROUP>/-/clusters

Confirmed/validated manually, example in screenshots.

MR acceptance checklist

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