feat: Add charset custom

[dliocode]

[dliocode]

`Why use:

const config = { host: '127.0.0.1', port: 3050, database: "/path/to/base.fdb", user: "SYSDBA", password: "masterkey", lowercase_keys: true, pageSize: 4096, retryConnectionInterval: 1000, encoding: 'WIN1252', charset: 'latin1' // Add new configuration - charset custom } `

[nickolasdeluca]

This is a neat feature that has been requested by the south american comunity, would be great to be able to stop modifying the source code of the package on production environments.