refactor: refactor persona into the wanted architecture - #1621

…ent#1651)

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### Description

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relevant motivation and context. List any dependencies that are required
for this change. -->

Adds the ability to mass-manage personas. Also adds the ability to
import personas from third party 'Pluralkit', to make usage of Sable in
replacement/alongside Discord easier for the user.

~~BLOCKED BY SableClient#1621~~

#### Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update

### Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings

### AI disclosure:

- [ ] Partially AI assisted (clarify which code was AI assisted and
briefly explain what it does).
- [ ] Fully AI generated (explain what all the generated code does in
moderate detail).
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