The `lsp-server` crate is currently published without license files, which is
needed when packaging in Linux distributions.
Symlink the files from the repository root so they are kept in sync.
Test showing the files get picked up by `cargo package`:
```
michel in rust-analyzer/lib/lsp-server on add-lsp-server-license [+] is 📦 v0.7.6 via 🐍 v3.12.1 (.venv311) via 🦀 v1.76.0
⬢ [fedora:39] ❯ cargo package --allow-dirty --no-verify
Updating crates.io index
Packaging lsp-server v0.7.6 (/home/michel/src/github/rust-lang/rust-analyzer/lib/lsp-server)
Updating crates.io index
Packaged 12 files, 59.6KiB (16.3KiB compressed)
michel in rust-analyzer/lib/lsp-server on add-lsp-server-license [+] is 📦 v0.7.6 via 🐍 v3.12.1 (.venv311) via 🦀 v1.76.0
⬢ [fedora:39] ❯ tar tf ../../target/package/lsp-server-0.7.6.crate | grep LICENSE
lsp-server-0.7.6/LICENSE-APACHE
lsp-server-0.7.6/LICENSE-MIT
```
Signed-off-by: Michel Lind <salimma@fedoraproject.org>
