Add deploy task support for DeployAt and DeployAtExpiry

[wlthomson]

Adds DeployAt and DeployAtExpiry inputs to the Deploy Release task (Deploy V6 and V7).

Prior to the replacement of the .NET CLI with the Executions API deprecation in V6, users could pass --deployAt and --deployAtExpiry as raw command line parameters via the now deprecated AdditionalArguments input. When the CLI was swapped out for the TypeScript client, these were not ported to first-class inputs.

Both inputs are optional (surfaced under "Additional Options") and accept ISO 8601 date-time strings.

[wlthomson]

Execution output snipped for a ADO pipeline with deployAt and deployAtExpiry parameters.

Resulting deployment task in the Octopus Deploy UI, with matching scheduled deployment time. The orange icon indicates that the task failed to run within the expiration window specified by the user.

[grace-rehn]

LGTM

Just a small question around error handling:
Would it be worth adding date format validation, or will an invalid format be caught server side? Just want to check its doesn't silently fail

[wlthomson]

LGTM

Just a small question around error handling: Would it be worth adding date format validation, or will an invalid format be caught server side? Just want to check its doesn't silently fail

Fair point.

There's no user-facing validation per se, so it depends on what we consider an error state and what we mean by "fail". Currently, if the parameters can't be parsed as a datetime (while we prompt for ISO 8601 for consistency, any datetime format will technically work), they will be treated as null and ignored.

To save us from future support requests, I'll add some basic error handling if the user doesn't specify a valid date.