add heroku 1-click deployment files

[rohitdash08]

This PR fixes #341

What kind of change does this PR introduce?

This PR introduces a feature that adds a Heroku 1-click deployment option using Docker. It includes configuration files such as app.json, heroku.yml, Dockerfile, and scripts for seamless deployment on Heroku using containers.

Why was this change needed?

This change was needed to simplify the deployment process for Postiz users. By introducing a Heroku 1-click deployment option, users can deploy the platform faster without manually configuring.

Other information:

I just gave it a try as it was pending for a long time, someone else is assigned to it but he's away for so long,

Checklist:

Put a "X" in the boxes below to indicate you have followed the checklist;

• [X] I have read the CONTRIBUTING guide.
• [X] I checked that there were not similar issues or PRs already open for this.
• [X] This PR fixes just ONE issue (do not include multiple issues or types of change in the same PR) For example, don't try and fix a UI issue and include new dependencies in the same PR.

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[jamesread]

Hey @rohitdash08 , thanks for the PR, I can see you've put some work into this.

I am worried about maintaining this going forward, as it duplicates another Dockerfile, another supervisord config, and similar. It also annoys me that ".deploy" is a weird name for a directory for Heroku!

1. Can Heroku just deploy existing container images? I would much rather a "1 click deploy" for the existing container images, as it's wayyy less to maintain going forward.
2. Can Heroku use something like a .heroku directory? .deploy is very generic.

[rohitdash08]

Hi @jamesread, I have made the changes can you please have a look?