add rust-analyzer to the toolchain

this should avoid the following error when trying to rust the LSP in a toolchain which does not have the rust-analyzer component and without running rustup component add rust-analyzer manually:

error: Unknown binary 'rust-analyzer' in official toolchain 'stable-x86_64-unknown-linux-gnu'.

rust-toolchain.toml

 [toolchain]
 profile = "minimal"
 channel = "1.78"
-components = ["rustfmt", "clippy"]
+components = ["rustfmt", "clippy", "rust-analyzer"]