Enhancement: isAWSProtonServiceAvailable signature should return Boolean

[niallthomson]

Currently the isAWSProtonServiceAvailable utility function ends up returning a string value, which means its necessary to do this in the most common use-case:

<EntitySwitch.Case if={e => Boolean(isAWSProtonServiceAvailable(e))}>

The function should return a Boolean to make its usage more convenient and follow the pattern of other similar Backstage utility functions like isGithubActionsAvailable (see GitHub Actions plugin):

<EntitySwitch.Case if={isAWSProtonServiceAvailable}>