chore(copilot-lua-cmp): alter accept line key mapping

[fynnfluegge]

Since cycling through basic cmp.nvim completions with <C-j>,<C-k> is a common usage, it feels more natural to map the copilot accept line action to one of the alternative (<C-n>,<C-p>) keymappings of cmp.nvim. Also since cycling with <Tab> is not possible if there is a copilot suggestion it becomes a bit inconvenient with the current mapping.

[github-actions]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• Proper usage of opts table rather than setting things up with the config function.