Add optional base64 decoding of mqtt.camera image

[TheHolyRoger]

Proposed change

The MQTT Camera integration has no support for encoded images, this PR adds optional b64 decoding

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

This PR resolves the complicated workarounds users have had to implement in order to decode b64 messages sent via MQTT and forward them on to HASS decoded, see this thread for various examples including whole nodered automations to solve this: https://community.home-assistant.io/t/blue-iris-motion-alerts-to-notification-with-image-in-home-assistant/363641/19

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io
• Add documentation for new encoding config for mqtt camera home-assistant.io#22622

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

• No score or internal
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• 🥇 Gold
• 🏆 Platinum

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[homeassistant]

Hi @TheHolyRoger,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[probot-home-assistant]

Hey there @emontnemery, mind taking a look at this pull request as it has been labeled with an integration (mqtt) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[emontnemery]

@TheHolyRoger Thanks a lot for linking to the forum thread showing why this is a useful addition 👍
Please open a documentation PR targeting the next branch.

[emontnemery]

Thanks, @TheHolyRoger 👍
Can be merged when a documentation PR is opened.

[TheHolyRoger]

Thanks @emontnemery ! Will do tomorrow when I get a min and will update the branch too

[TheHolyRoger]

@emontnemery done :)