This commit is fairly large and adds:

- client/pluginmanager/storagemanager
        This package handles runtime management of storageplugins,
        including fingerprinting.

- client/storage
        This package currently acts as a simple catalog of
        configurations for registered CSI plugins. It will eventually
        handle dispensing grpc clients.

- client/storage/csi
        This package adds a lightweight client around the CSI protobufs
        to give us a common place to handle CSI spec requirements and
        translating types into ones we can work with easily.

The remaining changes are plumbing to ensure that compontents are
correctly initialized

Initial support for Host Volumes

Co-Authored-By: Mahmood Ali <mahmood@hashicorp.com>

Check if driver handle is nil before execing

Defend against tr.getDriverHandle being nil.  Exec handler checks if
task is running, but it may be stopped between check and driver handler
fetching.

Update go-getter@1.1.0 to fix #3491

driver/docker: use default network mode

driver/docker: support unix destination mount path in windows

This reverts commit a6c96ead.

I missed this in #6051.

The `/v1/client/fs/stream endpoint` supports tailing a file by writing
chunks out as they come in. But not all browsers support streams
(ex IE11) so we need to be able to tail a file without streaming.

The fs stream and logs endpoint use the same implementation for
filesystem streaming under the hood, but the fs stream always passes
the `follow` parameter set to true. This adds the same toggle to the
fs stream endpoint that we have for logs. It defaults to true for
backwards compatibility.

fallback to docker default network mode instead of explicit bridge for linux
or nat for windows

Merge network namespaces work into master

Fix typo in Spreads key in JSON Job Specification

Update example setup to use non-deprecated join

Co-Authored-By: Mahmood Ali <mahmood@hashicorp.com>

Also includes unit tests for binpacker and preemption.
The tests verify that network resources specified at the
task group level are properly accounted for

Co-Authored-By: Michael Schurter <michael.schurter@gmail.com>