tooling: add gitignore entry for clangd's cache
tooling: add gitignore entry for clangd's cache

its possible to use clangd to parse the bpf code with the make target
`make -C bpf gen_compile_commands`.

once compile commands are present clangd will create a cache folder in
/bpf/.cache.

we don't ever want to check this in, and we don't need it showing up in
"git status".

Signed-off-by: Louis DeLosSantos <e7ae6d6e1769b56e461abca13c275680721e78d7@isovalent.com>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium