[Proposal] Set domain, tags etc. via the context

[mbark]

Having all fields for the error builder settable via context.Context would make it easy to make sure that any error further down in the chain has e.g., the domain set.

Motivation

For us the use case is that we have different areas of the code where it would be nice to always be able to ensure all errors have a domain or tags set.

Rather than enforcing everyone to remember to add In -- which sometimes might even be possible to figure out as you don't know what the call-chain is -- you set the In via the context and then as long as you do WithContext it will get set automatically.

Interface

In terms of interface I'm not sure what would be the best to avoid confusion. I can think of a few different ways

1. Prefixing with With.
2. Prefixing with WithContext.
3. Prefixing with Context.
4. Setting a default OopsErrorBuilder in the context.

(1) would have functions like WithIn. It has the advantage of being similar to other APIs when using context but doesn't play very nicely with the already existing function With (WithWith?).
(2) would have functions like WithContextIn. It is similar to the above but still sounds weird (WithContextWith?) and is maybe unnecessarily verbose without much clarity.
(3) would have functions like ContextIn or ContextTags which while not fully in line with what you would expect in therms of API doesn't collide with other names used and is also fairly clear what it would do.
(4) would need only two functions WithBuilder which sets a default builder in the context that can then be retrieved with FromContext(ctx).

Example

As an example of how it could look.

First of all, you add what you want to the context, using:

ctx := oops.WithBuilder(ctx, oops.In("domain"))

Then somewhere further down the call chain you then do

return oops.FromContext(ctx).Wrap(err)