Add support for mTLS (#470)

There is a need to secure the Action Cache for production builds which is
not possible with out authentication of the store.  This can be provided
by mTLS and the ability to make the action cache read only for some servers.

Cargo.Bazel.lock

@@ -1,5 +1,5 @@
 {
-  "checksum": "a6b16863ad5d0a1a72b20d57a7b103696e736e78f865de8cee087e4876a07970",
+  "checksum": "af852655d9eacd497a80742a4a6e9066b95c0a236ee1b77f438a7a8d7fef1237",
   "crates": {
     "addr2line 0.21.0": {
       "name": "addr2line",
@@ -9089,6 +9089,10 @@
               "id": "tokio-util 0.7.10",
               "target": "tokio_util"
             },
+            {
+              "id": "tonic 0.10.2",
+              "target": "tonic"
+            },
             {
               "id": "tracing 0.1.40",
               "target": "tracing"
@@ -15084,6 +15088,7 @@
         ],
         "crate_features": {
           "common": [
+            "default",
             "logging",
             "tls12"
           ],
@@ -15326,6 +15331,7 @@
             "default",
             "gzip",
             "prost",
+            "tls",
             "transport"
           ],
           "selects": {}
@@ -15384,10 +15390,22 @@
               "id": "prost 0.12.3",
               "target": "prost"
             },
+            {
+              "id": "rustls 0.21.10",
+              "target": "rustls"
+            },
+            {
+              "id": "rustls-pemfile 1.0.4",
+              "target": "rustls_pemfile"
+            },
             {
               "id": "tokio 1.35.1",
               "target": "tokio"
             },
+            {
+              "id": "tokio-rustls 0.24.1",
+              "target": "tokio_rustls"
+            },
             {
               "id": "tokio-stream 0.1.14",
               "target": "tokio_stream"