Update mini.surround repo URL

[auxym]

📑 Description

The repository for mini.surround has been moved from https://github.com/echasnovski/mini.surround to https://github.com/nvim-mini/mini.surround. This PR updates the URL and plugin name in the Readme and init.lua.

I also added a list of the default bindings which are set in the init.lua, as they differ from the default bindings of mini.surround (gz instead of s as prefix).

[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).

[azdanov]

Duplicate of #1635