fix(rust): preserve loading of rust-analyzer.json

[Ryex]

📑 Description

merge astrolsp settings in such a way as to preserve the default behavior of loading local project settings from rust-analyzer.json

ℹ Additional Information

The default behavior of rustaceanvim is to load a rust-analyzer.json at the project root to load rust-anlyzer settings
see:
rustaceanvim/config/server.lua#L15
rustaceanvim/config/internal.lua#L287

this file can have any of the keys defined in https://rust-analyzer.github.io/manual.html#configuration
either at the top level of the json or under a 'rust-analyzer' top level key

This is done by having server.settings be a function that takes the project root path and the default settings configured at server.default_settings and calling rustaceanvim's rustaceanvim.config.server.load_rust_analyzer_settings(root, opts) function.

This change configures rustaceanvim by merging the astrolsp configured opts around a similar function that itself merges the astrolsp configured settings table with the defaults before loading the rust-analyzer.json

as you can see, it's working as expected

[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.

[mehalter]

Looks great!