[Issue 271][Producer]Stop partition discovery on Close

[dvergnes]

Fixes #271

Motivation

This fixes a race when a producer is closed and the number of partitions changed i.e. the topic is deleted just after the producer is closed.

Modifications

It consists of stopping the ticker that controls the partition discovery in the background.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This is a trivial rework.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? no