Preprod-building workflow: input PR number instead of branch name

[Marc-Andrieu]

Description

Summary

The reason why

The new manually-triggered workflow to build&push pre-prods has a nice dropdown to select the pre-prod...
But the branch name had to be put in as a string.

Now you write the PR number.

Before/after comparison

• Before, it required the dev to search the branch name (which we often don't know), but we remember more easily PR numbers because shorter.
• A branch name is long thus prone to errors, a PR number is less error-prone
• There was no validation before, now a step ensures the PR number makes sense in the 1st place.

Technical details

The best would have been a nice dropdown (with branch names or PR numbers, whatever) because this ensures no error is possible and the dev doesn't have to search information.
But I did not find how to run some command before/inside the top-level on to generate the dropdown choices.

Issues to be resolved

Required PRs

Changes Made

You'd better read the code for this one.

Additional Notes

Classification

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 🔨 Refactor (non-breaking change that neither fixes a bug nor adds a feature)
• 🔧 Infra CI/CD (changes to configs of workflows)
• 💥 BREAKING CHANGE (fix or feature that require a new minimal version of the front-end)

• 😶‍🌫️ No impact for the end-users

Impact & Scope

• Other: CI/CD

Testing

• Tested on a fork, when the number has an opened PR and when not

Documentation

• No documentation needed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.89%. Comparing base (7dd1602) to head (549e6be).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #892   +/-   ##
=======================================
  Coverage   85.89%   85.89%           
=======================================
  Files         193      193           
  Lines       14953    14953           
=======================================
  Hits        12844    12844           
  Misses       2109     2109           

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