define freshness tiers for F# (#48008)

* define freshness tiers for F#

Define freshness tiers for different folders in the F# guide.

I followed the general strategy I used for C#:  Areas that are likely to need updates for each release based on new features are 1 year. Most reference is 3 years: Someone should give it a look, even if it's not likely that new features impact it.  Some of the reference for stable features is 5 years. Compiler diagnostics are 10 years.

* Update docfx.json

Co-authored-by: Tomas Grosup <[email protected]>

---------

Co-authored-by: Tomas Grosup <[email protected]>

Author: BillWagner

docfx.json

@@ -918,6 +918,16 @@
                 "docs/csharp/misc/**/**.{md,yml}": "3650-days",
                 "docs/csharp/roslyn-sdk/**/**.{md,yml}": "1825-days",
                 "docs/csharp/specification/**/**.{md,yml}": "1825-days",
+                "docs/fsharp/**/**.{md,yml}": "1095-days",
+                "docs/fsharp/whats-new/**/**.{md,yml}": "365-days",
+                "docs/fsharp/tools/fsharp-interactive/**/**.{md,yml}": "1095-days",
+                "docs/fsharp/scenarios/**/**.{md,yml}": "1095-days",
+                "docs/fsharp/tutorials/**/**.{md,yml}": "1095-days",
+                "docs/fsharp/tutorials/type-providers/**/**.{md,yml}": "1825-days",
+                "docs/fsharp/language-reference/**/**.{md,yml}": "1825-days",
+                "docs/fsharp/language-reference/compiler-messages/**/**.{md,yml}": "3650-days",
+                "docs/fsharp/style-guide/**/**.{md,yml}": "1095-days",
+                "docs/fsharp/get-started/**/**.{md,yml}": "1095-days",
                 "docs/framework/**/*.md": "3650-days",
                 "docs/iot/**/**.{md,yml}": "1825-days",
                 "docs/visual-basic/**/**.{md,yml}": "3650-days",