feat(tvix/store/blobsvc): add from_addr

This allows constructing blob stores with a URL syntax at runtime,
by passing the --blob-service-addr arg.

We probably still want to have some builder pattern here, to allow
additional schemes to be registered.

Change-Id: Ie588ff7a7c6fb64c9474dfbd2e4bc5f168dfd778
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8742
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/store/Cargo.toml

@@ -29,6 +29,7 @@ futures = "0.3.28"
 bytes = "1.4.0"
 smol_str = "0.2.0"
 serde_json = "1.0"
+url = "2.4.0"
 
 [dependencies.fuser]
 optional = true