Syntactic indexing: syntactic codeintel worker scaffolding

[keynmol]

Part of #58727

This PR scaffolds the new worker for syntactic batch indexing using Tree Sitter.
Currently the worker itself does nothing, only exposes a health endpoint and loads basic environment configuration.

• Bazel build for the Docker container
• Wire in scip-treesitter-cli to make it available in the container
• Dev setup for scip-treesitter-cli (copied from scip-ctags setup for local development)
• Run configuration for the worker sg run codeintel-syntactic-worker to test
• Start configuration sg start codeintel-syntactic - contains only the minimal dependencies required to run the worker, we will expand the configuration gradually as we add more features

Test plan

This is a scaffolding PR that contains no functionality yet.
The built docker image for the worker comes with a standard image_test

[varungandhi-src]

No major outstanding concerns apart from existing comments. Let's get this ball rolling.