Document next retry delay in .NET

[cretz]

What does this PR do?

Adds the .NET next retry delay, which is the .NET equivalent of the Java version at #2940.

[fairlydurable]

Suggested change

	### Overriding the retry interval with Next Retry Delay {#next-retry-delay}
	### Override the Retry interval with `NextRetryDelay` {#next-retry-delay}

• We use infinitive/base form, not present participle.
• When using specific code-derived terms, such as field names, use code face without spaces.

[cretz]

This is the form already present/approved at docs/develop/java/failure-detection.mdx and may be a rule worth applying consistently there too instead of just here (but feel free to apply here first)

[fairlydurable]

Suggested change

	You may throw an [Application Failure](/references/failures#application-failure) with the NextRetryDelay field set. This value will replace and override whatever the retry interval would be on the retry policy.
	When you throw an [Application Failure](/references/failures#application-failure) and assign the `NextRetryDelay` field, its value replaces and overrides the Retry interval defined in the active Retry Policy.

• Retry and Retry Policy are reserved terms (see Vale list)
• Consider adding where it was thrown from, "When you throw...from an Activity, and assign the..."
• What is the active Retry Policy for? An Activity Handle/Stub that called this Activity? Consider adding "in the active Retry Policy for the...."

[cretz]

This is the form already present/approved at docs/develop/java/failure-detection.mdx and may be a rule worth applying consistently there too instead of just here (but feel free to apply here first)

[fairlydurable]

Suggested change

	For example, if in an activity, you want to base the interval on the number of attempts, you might do:
	For example, you might scale the next Retry delay interval based on the current number of attempts.
	Here's how you'd do that in an Activity:

• Activity is a reserved term, so capitalized

[cretz]

This is the form already present/approved at docs/develop/java/failure-detection.mdx and may be a rule worth applying consistently there too instead of just here (but feel free to apply here first)

[fairlydurable]

It may be "obvious" by name and context that this is "retrieve attempt count from the Activity Execution context", but a comment wouldn't hurt, and ditto below, "Update the next Retry delay by assigning a Time value to the nextRetryDelay field"

Also, this uses lower case n for Next. Is the material preceding incorrect?

[cretz]

but a comment wouldn't hurt, and ditto below

This is the form already present/approved at docs/develop/java/failure-detection.mdx and may be a rule worth applying consistently there too instead of just here (but feel free to apply here first)

Also, this uses lower case n for Next. Is the material preceding incorrect?

Yes

[cretz]

Note, this just copies content from already-approved/published Java and does the slightest alterations for .NET so as not to change what was already approved. Feel free to change what is needed there and here. We made this PR in a branch on the repo itself instead of in a fork so it could be edited by docs before merge.