Template variables support for release-pr branch name

[AdamStrojek]

Motivations

Currently we can provide static text as pr_branch_prefix in config file. This solution is not that flexible, and requires using suggested branch naming strategy. I think it would be better to replace it with template system that allows you on providing such configuration:

[workspace]
pr_branch_template = "release/v{{ version }}"

If somebody wants to remain current behavior we can leave pr_branch_prefix as legacy option that would automatically be interpreted as:

[workspace]
pr_branch_template = "{{ pr_branch_prefix }}-tmp-{{ date }}"

If instructed I can implement this feature

[marcoieni]

I agree with you that pr_branch_template is better than pr_branch_prefix.
The issue is that release-plz in workspaces has more {{ version }}s. What should release-plz put in that variable in this case?

Plus, the version could change (e.g. because there's a new breaking change and so instead of 0.4.1 is now 0.5.0). The branch will change so release-plz needs to close and open a new PR. So much complexity added! Is it worth it? Why is the current prefix not good enough for your purposes?