Backend: API endpoint to change global user roles for admin

[manjitapandey]

Is your feature request related to a problem? Please describe.
As discussed in the last user management meeting and followed by #1083 , currently we have 3 global roles namely, mapper, admin and blocked users. We lack specific endpoint to change global user roles.

Describe the solution you'd like
An API endpoint to change global user roles for admin.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[spwoodcock]

Rather than an endpoint specific to admins, this should have a field admin level permission set.

Roles only really make sense related to a project, so this should take a project id.

Project managers, assistant admins, field admins, should all be able to update roles.

But they can only assign roles of equal level or below their own role!

[spwoodcock]

Sorry I read your description more carefully.

The global roles are only there to create new admins or block users, which are infrequent activities.

I guess an endpoint for this could make sense, but adding a frontend page to manage it afterwards might be overkill (I don't imagine it will be used much). But if its a tiny effort, I guess why not!