feat(copilotchat-nvim): select a picker based on installed one

[azdanov]

📑 Description

This removes mandatory dependency on telescope and selects the picker based on which one is installed instead with a default to the telescope.

ℹ Additional Information

Can see different integrations here:
https://github.com/CopilotC-Nvim/CopilotChat.nvim/tree/main/lua/CopilotChat/integrations

[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)

• Entry returns a single plugin spec with the new plugin as the only top level spec (not applicable for recipes or packs).

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

• Proper usage of specs table for all specs that are not dependencies of a given plugin (not applicable for recipes or packs).

[Uzaaft]

Gonna mark this as draft until docs are added just to safeguard our own sanity.

[azdanov]

Also would give time for any bugs to get fixed on their side

[tku137]

Done here CopilotC-Nvim/CopilotChat.nvim#726

[tku137]

A follow-up refactor based on this PR: #1337