fix(java): use jdtls for formatting instead of clang-format

[Juniar-Rakhman]

📑 Description

In the java pack, clang_formatter is unnecessary. It also overrides the formatting capability of "mfussenegger/nvim-jdtls".

Having clang_formatter for java pack does not make sense, as the default formatter works just fine.

list of changes:

• removed unnecessary clang_formatter and everything related to it.
• updated readme to include custom formatter example.

[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]

LGTM