Manually change user's reputation

In some situations, it is necessary to manually adjust a user's reputation:

1. Increase the reputation of someone to grant them specific privileges.
2. Decrease the reputation of someone as a form of punishment.

Need to select user and input the reputation change value, such as `n` or `-n`, along with the reason for the adjustment.

## Plugin info

Name: Reputation change
Description: Manually change user's reputation.

## Plugin forms

- Username
- Change reputation value
- type 10 means increasing reputation by 10
- type -15 means decreasing reputation by 15
- Reason for change
- The reason will show in public


No files, tests, or entry points are named. Start with the requested plugin forms: user selection, signed reputation change value, and public reason; the work is done when manual increases and decreases can be recorded for a selected user with that reason visible.

Written by the indexing model from the issue text.