codeintel: Support multipart LSIF index uploads
Created by: efritz
This implements RFC 143: Multipart uploads.
Overview of changes:
- Bundle manager now has two new endpoints: one to upload a partial index, and one to stitch together many partial indexes into a single compressed file.
- The api server now supports additional query parameters for its upload endpoint. These query parameters are supplied via src-cli (as of https://github.com/sourcegraph/src-cli/pull/197).