Increase embed column lengths to 256

[biast12]

The embed title, author_name and fields name have a limit of 256, which currently in the database is 255
https://docs.discord.com/developers/resources/message#embed-object:~:text=should%20display%20inline-,Embed%20Limits,-To%20facilitate%20showing

This is mostly just for the SQL query but it needs to be added in the code too

ALTER TABLE embed_fields ALTER COLUMN "name" TYPE VARCHAR(256);
ALTER TABLE embeds ALTER COLUMN "title" TYPE VARCHAR(256);
ALTER TABLE embeds ALTER COLUMN "author_name" TYPE VARCHAR(256);