[enhancement] Proper permission in qembed

[rtk-rnjn]

https://discord.com/channels/746337818388987967/829945992048148480/1125454819012911164

i guess bot should also check if the invoker has permission to send message, embed links, and attachfiles in the target channel

[deadaf]

fixed with #147, kind of messed up. @Vader-OP fixed two issues in a single PR.