Add preserve-resources flag

[allisonlarson]

Description

Adds a --preserve-resources flag when running a job to preserve the task resources when updating an existing job. In situations where the resources of a task were updated separately, like via nomad-autoscaler, the job can still be deployed and choose to keep those configurations.

Testing & Reproduction steps

Added unit tests, and tested flag manually by running the DAS autoscaler

Links

internal ref: https://hashicorp.atlassian.net/browse/NMD-870

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad website documentation to reflect this. Refer to
  the website README for docs guidelines. Please also consider whether the
  change requires notes within the upgrade guide.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

[aimeeu]

minor nit - thanks for updating the docs!

[aimeeu]

Suggested change

	- `-preserve-resources`: If set, the existing task resources will be preserved
	- `-preserve-resources`: If set, the existing task resources are preserved

change to present tense, and also to match other entries

[aimeeu]

doc content look great - thank you!

[tgross]

LGTM!

I think if we could do it over again we'd probably figure out a better way to split up the declarative job spec from the ephemeral job state, and stick the scaling counts in the job state. And that's informing the awkwardness of having to wrap the upsertJobImpl this way where we're pushing the request down to the state store. We could rewrite every caller of UpsertJob to take a request (similar to other methods) but that's hundreds and hundreds of new lines of test code where we're making up a request to contain the job and don't care about these flags. Not worth the added test complexity everywhere.

[github-actions]

I'm going to lock this pull request because it has been closed for 120 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.