Add details about region

[abbycross]

Closes #3857

CC: @kevin-stevens-ibm @francabrera We can use this PR to expand on the information about regions in the docs. I've begun by making a couple of additions to the FAQ and Instances pages. Feel free to add comments or an outline of the new Regions page you'd like to see - and let me know where in the table of contents we should put it - maybe under IBM Quantum Platform?:

[kevin-stevens-ibm]

I feel like a regions page should go under 'IBM Quantum Platform' and then could go under

• Set up IBM Quantum Platform
• Accounts, access groups, and policies
• Work with instances

But isn't perfect in any of those places 🤷

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For an outline I think we can do something like

What are Regions

Regions represent the physical location of the resources used to service your requests. The IBM Cloud region and data center locations for resource deployment page provides a good overview of this concept. Note that IBM Quantum only operates out of a subset of all IBM Cloud regions.

Why use Regions

Regions allow users to maintain better governance on where users data flows.

Circuit inputs and outputs stay within the region they were submitted.

The API is regional when the access path uses Virtual Private Endpoints. However, the platform frontend is served globally, so any data retrieved or submitted via the Platform UI may cross a regional boundary.

Note that the Identity and Access Management (IAM) service operates on a global level and data may flow into any IBM Cloud region even beyond the IBM Quantum deployed regions.

Changing Regions

In order to switch between regions, use the region switcher dropdown in the top menu.

<INSERT A PICTURE OF THE SWITCHER>

Regional Separation

Given the fact that regions represent physical resource locations, it follows that the physical quantum computes are associated with only a single region. In order to submit jobs to a particular quantum computer, one must have an instance with available capacity in that region (see page on instances).

Capacity is also allocated on a regional basis. In order to adjust the split of capacity between regions, please create a support ticket with the desired updated split