* artifact: enable inheriting environment variables from client
This PR adds client configuration for specifying environment variables that
should be inherited by the artifact sandbox process from the Nomad Client agent.
Most users should not need to set these values but the configuration is provided
to ensure backwards compatability. Configuration of go-getter should ideally be
done through the artifact block in a jobspec task.
e.g.
```hcl
client {
artifact {
set_environment_variables = "TMPDIR,GIT_SSH_OPTS"
}
}
```
Closes#15498
* website: update set_environment_variables text to mention PATH
This PR adds the client config option for turning off filesystem isolation,
applicable on Linux systems where filesystem isolation is possible and
enabled by default.
```hcl
client{
artifact {
disable_filesystem_isolation = <bool:false>
}
}
```
Closes#15496
Fix numerous go-getter security issues:
- Add timeouts to http, git, and hg operations to prevent DoS
- Add size limit to http to prevent resource exhaustion
- Disable following symlinks in both artifacts and `job run`
- Stop performing initial HEAD request to avoid file corruption on
retries and DoS opportunities.
**Approach**
Since Nomad has no ability to differentiate a DoS-via-large-artifact vs
a legitimate workload, all of the new limits are configurable at the
client agent level.
The max size of HTTP downloads is also exposed as a node attribute so
that if some workloads have large artifacts they can specify a high
limit in their jobspecs.
In the future all of this plumbing could be extended to enable/disable
specific getters or artifact downloading entirely on a per-node basis.
