[FIX] webservice: deprecate implicit content_only=True default

[HasanAlsaafen]

Fixes #142

Problem

BaseRestRequestsAdapter._request() defaults content_only to True,
returning raw bytes instead of the expected requests.Response object.
This violates the Principle of Least Astonishment, as most HTTP client
libraries return a Response object by default.

Additionally, BackendApplicationOAuth2RestRequestsAdapter._request()
ignored content_only entirely, always returning .content, which was
inconsistent with the base adapter.

Solution

• content_only now defaults to None. When not explicitly set, a
  deprecation warning is logged and the current behavior (True) is
  preserved for backward compatibility.
• Fixed the OAuth2 backend application adapter to respect content_only
  consistently with the base adapter.
• Added tests covering: default behavior with warning, explicit
  content_only=True, and explicit content_only=False.

Testing

All 25 existing tests pass alongside the 3 new tests added.

[OCA-git-bot]

Hi @etobella,
some modules you are maintaining are being modified, check this out!

[Ricardoalso]

Hey @HasanAlsaafen, thanks for this PR related to #142.

I originally opened the issue to gather external input on how to handle this situation, if we decide to address it. The challenge with making changes like the ones introduced in this commit is that they may disrupt the expected behavior of existing modules or code that depend on the current default, potentially breaking running instances.

[HasanAlsaafen]

Hey @Ricardoalso
Thanks for raising this, it's a valid concern.

Before deciding how to proceed, it might help to first get a clearer picture of the actual impact: are there known modules in the OCA ecosystem that rely on the current default behavior, or would this mainly affect external/custom code outside OCA? If we can narrow down who is likely affected, it'll be easier to choose between an opt-in flag, a deprecation cycle, or a straight breaking change with a migration note.

Let me know if there's a preferred way to check this (e.g. searching OCA repos for usages), and I can help gather that data before we settle on an approach.

[simahawk]

@HasanAlsaafen sounds like a good approach. Can you pls rewrite the commit msg as [FIX] webservice: deprecate implicit content_only=True default.
Regarding other modules: I don't know any other module in the OCA that directly relies on webservice.call but you could search for modules depending on it.
Last but not least. pls check the CI 🙏