Adds the ability to upload a custom document when using a template.
This is useful when you have a given fixed template with placeholder
values that you want to decorate with Documenso fields but will then
create a final specialised document when sending it out to a given
recipient.
Checkboxes were previously styled super wonky due to
the usage of checkboxClassName which styled the checkbox
trigger.
This change reverts all that and leaves it with sensible defaults
across dark and light mode.
Passes the timezone of the user uploading the document/template via the
UI to the server.
If the user uploads a document/template via the API and doesn't set a
timezone, it defaults to `Etc/UTC`.
## Description
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## Related Issue
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## Changes Made
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## Testing Performed
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## Checklist
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- [ ] I have tested these changes locally and they work as expected.
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