Deprecation notice for API versions 1.0 to 2.0

[Flix6x]

• Start logging warnings whenever users call endpoints in the API blueprints 1.0, 1.1, 1.2, 1.3 and 2.0.
• Add release notice for FlexMeasures hosts (example follows).

With flexmeasures==0.12 we start logging warnings whenever users call endpoints in the API blueprints 1.0, 1.1, 1.2, 1.3 and 2.0. With flexmeasures==0.13 users still calling these endpoint will receive a deprecation notice.

[nhoening]

I'd aim to remove the endpoints in 0.13, so in 0.12 I'd send both notices, to API users and to hosts (per log)

[Flix6x]

How would you send notices to API users?

One option is to add it as a message to the response, but I suspect that such messages will not be noticed, unless the response causes a failure down the line.

Or would you email the user?

[nhoening]

The former solution. Hosts can mail users they see in the logs, otherwise they get too many emails. We should use Sentry for our logging as well, that's easy to filter.

[Flix6x]

Just to be clear, I don't want responses in 0.12 to cause failures down the line. Just adding the notice as an extra message to the response already seems fine, though.

[Flix6x]

While putting in the work for this PR, I discovered that the recommended way of adding deprecation notices is not through the response message, but rather through the response headers. There are dedicated fields for deprecation and sunsetting, which are at various levels of maturity of becoming an Internet Standard.

Eric Wilde published on the matter: https://goodapi.co/insights/deprecation-and-sunsetting