This commit adds the `pricePerGateway` flag and deprecates the `pricePerBroadcaster` flag
per core team decision (details:
https://discord.com/channels/423160867534929930/1051963444598943784/1210356864643109004).

This commit removes the `PricePerBroadcaster` deprecation comment since
this is already clear from the glog warning below.

This commit ensures that the deprecation condition for the `pricePerBroadcaster`
flag properly handles the default empty string value.

This commit ensures that the `pricePerGateway` is correctly used instead
of the `pricePerBroadcaster` when it is set.

…of 'gateways'

This commit updates the configuration to replace the `broadcasters` property
specified under the `pricePerGateway` flag with `gateways`. Additionally, it
ensures that a warning is issued when the deprecated property is still used.

This commit ensures that the TestParseGetBroadcasterPrices function uses
the new getGatewayPrices function.

This commit updates the `TestParseGetBroadcasterPrices` function to
`TestParseGetGatewayPrices` to align with the new node naming convention.