[UBP] Replace "pay-as-you-go billing" with "billing" in personal and team billing settings

[jldec]

The extra qualification of "pay-as-you-go billing" for billing pages in the dashboard is unnecessary, since this is the only type of billing available.

Suggest: "Manage billing for your Gitpod user account."

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Suggest: "Manage billing for your Gitpod team."

cc: @gtsiolis

[gtsiolis]

@jldec Would it make sense to go with something like the following to differentiate the team billing from the personal billing? Optionally, we could also inject other actions available through this section like setting usage limit.

Manage billing for your team.

Manage billing for your personal account.

This could provide a subtle hint to help users associate this page better with their personal account which can be currently. confusing sometimes (see #15012), etc. and help us avoid having specific page titles like we do with the usage page.