Remove legacy image scaling options

[pyby]

Motivation and Context

Integration Layer product has deprecated endpoints, which will be removed during migration to the new major version (named SAM): Services to transform images.

In addition:

• SRF business unit image service will remove the scaling support in 2023 Q4.
• RTS business unit image service does not work as expected with PlaySRG image service, regarding the aspect ratio given within the url. Will be fix in 2023 Q3.

The ImageServices has to be updated accordingly.

Main new image service to use is the PlaySRG image service.

Description

• Remove all "aspectRatio" scaling options.
• Introduce SRGScalingService to use business unit scaling services or the centralized Integration Layer one.
• Use PlaySRG image service by default, expect for rts.ch host with .image in the path, which still use the BU image service. See https://github.com/SRGSSR/srgdataprovider-apple/issues/47
• Update Unit tests with expected 16:9 ratio.
• Update Get Started and Service Availability documentations.
• Breaking changes API: New major version.

Checklist

• [x] The branch should be rebased onto the develop branch for whole tests.
• [x] The documentation has been updated (if relevant).
• [x] Issues are linked to the PR, if any.

[defagos]

Before having a more comprehensive look at the code, just a few clarification questions:

1. Do we still really need to provide access to the /scale/width services? Isn't the new endpoint sufficient?
2. If yes:
   • Which name could we find so that API usage is easy? I am not sure that just looking at the API makes it easy to know when each kind of service needs to be applied. Previously the intent was clear (scaling behavior) but now this context has disappeared and I am not sure why, as a user, I should use one service rather than the other.
   • Why should the BU scaling service be the default? Shouldn't we move away from it?

[pyby]

Before having a more comprehensive look at the code, just a few clarification questions:

1. Do we still really need to provide access to the /scale/width services? Isn't the new endpoint sufficient? […]
   • Why should the BU scaling service be the default? Shouldn't we move away from it?

After discussions with RTS colleagues, the RTS image service will support ratio in url in 2023 Q3, not before. The PlaySRG image service keeps the image ratio given by the url, which is today for RTS a "raw" image ratio: unexpected image ratios are returned.

To move on, the new proportion:

• The library knows internally which image service to use, and does not expose it through the public API.
• When RTS will release its new image service, SRGDataProvider+ImageURLs.m will be updated to use only PlaySRG image service.