chore: extract deploying to staging in `cd` workflow

[Max Kalashnikoff | maksy.eth]

At the moment we can deploy only to the staging and prod environment together in our cd and auto_deploy workflows without the choice to deploy only to the staging environment.
Also, auto-deploy is triggered on merge and running deploying to the prod (without running release, example), so every merge the release is deployed to the prod without running release itself.

My proposal is:

• auto_deploy on merging will deploy only to the staging,
• cd can be triggered manually with the choice to deploy on the staging only or to both, as we already have in blockchain-api,
• release triggering only manually and running cd with deploying to staging and prod.

[Max Kalashnikoff | maksy.eth]

The ability to send a branch to the staging is good for testing purposes, like testing #219 without deploying and touching prod.