Allow bridge configuration to be reloaded

[abiliojr]

I created a pull request (https://github.com/eclipse/mosquitto/pull/1698) with the required changes to reload the bridges' configuration.

My implementation drops all exiting bridges while reloading. I am not sure if this is the desired behavior.

Here are some ideas if more control is needed. I might add an argument to the bridge, called "action_on_reload", with 3 potential options:

• immediate
• lazy (take values on next re-connection) [default?]
• load_subscriptions (same as lazy, but subscription changes take effect immediately)

My first attempt was to implement it this way, but it became a bit too entangled for my taste. Please advice.

[abiliojr]

I've just updated the pull request. For now it can take 2 options: lazy and immediate. I made lazy the default. Any suggestions?

[strahlc]

The mentioned pull request was merged to develop five years ago.

Is there a reason not to release this change?

Because AWS does not support wild cards when subscribing to retained topics, i have to change my bridge config quite often and then i always need to restart mosquitto. I would be so much nicer to just send a reload signal to reload the bridge topics.