Is there a way to send a message to someone/everyone in the server from the console?

From this answer to "How To Get Command Blocks Talking in Chat", linked originally by pppery:

The /tellraw command, syntax /tellraw <json compound array/singleton> displays a message in chat, but it gives you full customization of its output from color to formatting using json formatting.

A command block with /tellraw @a {"text":"Hello World!"} would output:

Hello World!

(Note that I have omitted some of the answer and kept the part of it I think you should go with - the tellraw command)

By the way, aytimothy also linked to minecraftjson.com, which is a useful site for generating tellraw commands.