fix : desired_status backfill in deployments table

[k-anshul]

The desired_status column was added a few releases back where the default desired_status is 0(unspecified).
For deployments that were created before the release the desired_status is set to 0.
In the last release the desired_status of running deployments in normal reconcile operations is set to current desired_status:

rill/admin/deployments.go

Lines 94 to 95 in bd1e43b

	func (s *Service) UpdateDeployment(ctx context.Context, depl *database.Deployment, branch string) error {
	// Update the deployment with the new branch (or existing branch) and set existing desired status to retrigger reconcile flow

This is leading to reconcile being no-op for many existing deployments.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!