feat(sql): disable sqls formatter and add sqlfluff

[azdanov]

Closes #1323

📑 Description

This should disable the sqls lsp formatter and use sqlfluff instead. Might as well use sqlfluff diagnostics also, I see them beneficial.

This is the issue with sqls at the moment: sqls-server/sqls#149

ℹ Additional Information

This needs thorough testing, since I'm not sure if all works as expected and I lack knowledge to verify on my own due to being new to neovim ecosystem. Especially different combinations of null-ls/conform/nvim-lint/lspconfig community packs.

I disabled cwd in conform due to default settings requiring a config file to be present for the formatter to work. I didn't notice this behavior in null-ls.

There might be an issue with timeouts for formatting, since I've noticed in other github repos people put 1s or even 5s timeout when using sqlfluff.

[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]

Seems to be working. One thing is that the default conform timeout in community pack is 500ms, which might not be enough for sqlfluf 🤷‍♂️

[mehalter]

LGTM!

[mehalter]

Oh actually, can you update the README