deb: Set utf8 encoding for MCP database

[mamedin]

This PR adds the following features:

• Use dbc_mysql_createdb_encoding="UTF8" to create database with UTF8 enconding.
• Remove /etc/dbconfig-common/archivematica-mcp-server.conf file when purging archivematica-mcp-server package.
• Prompt when removing archivematica-mcp-server package, asking for MCP database deletion.
• Add dbconfig-mysql dependency to archivematica-mcp-server package.

Connects to https://github.com/archivematica/Issues/issues/505