[Feature Request]: Make backend URL customisable to the user

[dmohns]

Preflight Checklist

• I have read the Contributing Guidelines for this project, if it exists.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Problem Description

Currently, the backend URL is hardcoded into the APK.

Users need to be able to customise the URL to be able to use difference instances of the MPM backend.

Proposed Solution

A settings dialog where the user can enter a URL. Default value should be https://demo.micropowermanager.io/#/

Alternatives Considered

N/A

Additional Information

No response