use dedicated exec group for link actions

When remote execution is used, a user may want to use different
exec properties for different actions under the same target.

For example:

A go_test could include 3 different actions:
- GoCompilePkg
- GoLink
- GoTest

If users wish to use a special exec_properties for GoLink actions,
after this PR, they could do so with:

```python
go_test(
  ...
  exec_properties = {
    # Default
    "container-image": "docker://alpine",
    "EstimatedMemory": "500MB",

    # Only applied to GoLink exec_group
    "GoLink.container-image": "docker://ubuntu",
    "GoLink.EstimatedMemory": "2GB",
  }
  ...
)
```

Reference: https://bazel.build/extending/exec-groups

go/private/actions/BUILD.bazel

@@ -55,6 +55,7 @@ bzl_library(
         "//go/private:common",
         "//go/private:mode",
         "//go/private:rpath",
+        "//go/private/rules:execgroup",
         "@bazel_skylib//lib:collections",
     ],
 )

go/private/actions/link.bzl

@@ -33,6 +33,10 @@ load(
     "@bazel_skylib//lib:collections.bzl",
     "collections",
 )
+load(
+    "//go/private/rules:execgroup.bzl",
+    "LINK_EXEC_GROUP",
+)
 
 def _format_archive(d):
     return "{}={}={}".format(d.label, d.importmap, d.file.path)
@@ -206,6 +210,7 @@ def emit_link(
         inputs = inputs,
         outputs = [executable],
         mnemonic = "GoLink",
+        exec_group = LINK_EXEC_GROUP,
         executable = go.toolchain._builder,
         arguments = [builder_args, "--", tool_args],
         env = go.env,

go/private/rules/BUILD.bazel

@@ -42,6 +42,7 @@ bzl_library(
         "//go/private:mode",
         "//go/private:providers",
         "//go/private:rpath",
+        "//go/private/rules:execgroup",
         "//go/private/rules:transition",
     ],
 )
@@ -56,6 +57,14 @@ bzl_library(
     ],  # keep
 )
 
+bzl_library(
+    name = "execgroup",
+    srcs = ["execgroup.bzl"],
+    visibility = [
+        "//go:__subpackages__",
+    ],
+)
+
 bzl_library(
     name = "info",
     srcs = ["info.bzl"],
@@ -131,6 +140,7 @@ bzl_library(
         "//go/private:mode",
         "//go/private:providers",
         "//go/private/rules:binary",
+        "//go/private/rules:execgroup",
         "//go/private/rules:transition",
         "@bazel_skylib//lib:structs",
     ],

go/private/rules/binary.bzl

@@ -35,6 +35,10 @@ load(
     "//go/private/rules:transition.bzl",
     "go_transition",
 )
+load(
+    "//go/private/rules:execgroup.bzl",
+    "RULES_GO_EXEC_GROUPS",
+)
 load(
     "//go/private:mode.bzl",
     "LINKMODES",
@@ -414,6 +418,7 @@ _go_binary_kwargs = {
             default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
         ),
     },
+    "exec_groups": RULES_GO_EXEC_GROUPS,
     "toolchains": [GO_TOOLCHAIN],
     "doc": """This builds an executable from a set of source files,
     which must all be in the `main` package. You can run the binary with

go/private/rules/execgroup.bzl

@@ -0,0 +1,5 @@
+LINK_EXEC_GROUP = "GoLink"
+
+RULES_GO_EXEC_GROUPS = {
+    LINK_EXEC_GROUP: exec_group(),
+}

go/private/rules/test.bzl

@@ -44,6 +44,10 @@ load(
     "//go/private/rules:transition.bzl",
     "go_transition",
 )
+load(
+    "//go/private/rules:execgroup.bzl",
+    "RULES_GO_EXEC_GROUPS",
+)
 load(
     "//go/private:mode.bzl",
     "LINKMODES",
@@ -443,6 +447,7 @@ _go_test_kwargs = {
     },
     "executable": True,
     "test": True,
+    "exec_groups": RULES_GO_EXEC_GROUPS,
     "toolchains": [GO_TOOLCHAIN],
     "doc": """This builds a set of tests that can be run with `bazel test`.<br><br>
     To run all tests in the workspace, and print output on failure (the