add .prettierignore and/or format additional files

[sethvincent]

I've noticed some files that haven't been formatted with prettier. Some of them (generated files) seem like they don't need to be and should be ignored:

 CHANGELOG.md                            
 drizzle/client/meta/0000_snapshot.json  
 drizzle/client/meta/_journal.json       
 drizzle/project/meta/0000_snapshot.json 
 drizzle/project/meta/_journal.json      
 src/generated/extensions.d.ts           
 src/generated/extensions.js             
 src/generated/extensions.ts             
 src/generated/keys.d.ts                 
 src/generated/keys.js                   
 src/generated/keys.ts                   
 src/generated/rpc.d.ts                  
 src/generated/rpc.js                    
 src/generated/rpc.ts                    

I'd probably ignore everything but the change log.