Update docs to cover new capabilities added by: bazel-contrib/bazel-gazelle#1776

Closes #3935

Docs for bazel-contrib/bazel-gazelle#1731

The community has agreed[1] that "pure" builds of Go code should
use the `purego` build tag.

This change adds that de-facto tag.

The minimum version of Gazelle is bumped to `0.36.0` which includes a patch[2]
for ignoring the `purego` tag so that the source flies are passed to the
compiler for conditional compilation decisions.

[1]: golang/go#23172
[2]: bazel-contrib/bazel-gazelle#1767

This gives us a determinstic location to ignore for goleak, which we
previously had, but was removed as part of #3920.

…3919)

* Add support for `--incompatible_enable_proto_toolchain_resolution`

* Do not use dict union

* Fix visibility

* Fix buildifier finding

* Add proto deps to tests

* Attempt to fix integration tests

* MOre fixes

* Add test deps

* Fix test sources

* Remove unused load

* Fix tests and update to rules_proto 6.0.0

* Add back WORKSPACE deps

go_tool_binary() is completely oblivious of toolchains. The reason being
that Go toolchains actually depend on their output. Adding a toolchain
dependency would thus add a cyclic dependency. This is problematic,
because it means that the actions with mnemonic GoToolchainBinaryBuild
end up getting scheduled on arbitrary workers.

Address this by adding exec_compatible_with to the locations where
go_tool_binary() is instantiated, namely the auto-generated BUILD files
that are part of Go SDKs.

Fixes: #3942

This PR prepares a minor release to allow downstream users to begin integrating with #3919