Fix UI issues after introducing new button design system

[bl-nero]

This PR:

• fixes minor UI issues, mostly margins and capitalizations
• changes button height on the login form, but doesn't yet address the full scope of design changes for the SSO buttons (awaiting final opinion from the UX team)
• replaces resource enrollment buttons with something that doesn't look like a CTA if the resource lists are not empty
• adds intent indications to the file transfer requests UI

Caveat: since we are abandoning button capitalization, existing SSO buttons may look weird for those who have all-lowercase names of their SSO connectors. We may need to issue an announcement to our users about using the displayName connector property to fix this.

Before	After

Closes https://github.com/gravitational/teleport/issues/43175

[github-actions[bot]]

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