Use declarative approach for scripts

[gpsaggese]

Many times we want to reach a state (e.g., add people to a certain repo, set a set of labels in a repo, ...). For this kind of work, we want to use a paradigm like:

• Specify the state we want to reach
• The script understands what's the different between the current and target state
  • E.g., we want to have N people added to the repo, but now there is a subset M of them -> so we need to add N - M
• A --dry-run mode allows to see / validate the plan
• A --backup mode saves the state before changing it
• When we run the script, a log with the summary of what was done is generated to inspect

This is an extension of our incremental / idempotent approach.

• It also makes it easy to roll back changes (using --backup)

We should:

• [ ] Document it somehow
• [ ] Write the new scripts to use this approach
• [ ] Start back porting the old scripts

FYI @heanhsok @Shaunak01 @Shayawnn @indrayudd @tkpratardan @aver81 @aangelo9 @madhurlak0810 @sandeepthalapanane

[gpsaggese]

Let's assign it to @sandeepthalapanane since a couple of his scripts can use this approach (the repo sync and managing the GH invites)