Add a context manager for temporarily adding extras to StdlibLogger

[sethmlarson]

Similar to how structlog provides .bind() we could provide a context manager that adds extras so you don't have to include them every time you call .info(), etc.

[Divyadarshee]

@sethmlarson what is the current way to add extra without including them in every log call?

[Divyadarshee]

@sethmlarson can something like this be possible with the current version
log example:
addItem='abcd'
logger.info(f"added todo item {addItem} to the todo list")
log:
{'name': 'app.routes.controller', 'msg': 'added todo item abcd to the todo list', 'args': (), 'levelname': 'INFO', 'levelno': 20, 'fields': {'addItem': 'abcd'}}