Allow Log.with_context to set context

[caspiano]

Feature Request

• Is your feature request related to a problem? Please describe clearly and concisely what is it.

It's pretty common when using logging contexts to do something like the following (it's even in the docs)

::Log.with_context do
  Log.context.set some_data: 12345
  ...
end

• Describe the feature you would like, optionally illustrated by examples, and how it will solve the above problem.

I think Log.with_context should be able to set the context for the block.

::Log.with_context(some_data: 12345) do
  ...
end

• Describe considered alternative solutions, and the reasons why you have not proposed them as a solution here.

As stated above.

• Does it break backward compatibility, if yes then what's the migration path?

Nope