API Coverage: Add Support for Deployment Environments (#395)

Adds the following new cmdlets for managing GitHub Deployment Environments:

- `New-GitHubDeploymentEnvironment`
- `Get-GitHubDeploymentEnvironment`
- `Set-GitHubDeploymentEnvironment`
- `Remove-GitHubDeploymentEnvironment`

Fixes #394

#### References

-  [Deployment Environments](https://docs.github.com/en/rest/deployments/environments)

Formatters/GitHubDeployments.Format.ps1xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Configuration>
+  <ViewDefinitions>
+    <!--=============== GitHub.DeploymentEnvironment Type View ===============-->
+    <View>
+      <Name>GitHub.DeploymentEnvironment</Name>
+      <ViewSelectedBy>
+        <TypeName>GitHub.DeploymentEnvironment</TypeName>
+      </ViewSelectedBy>
+      <TableControl>
+        <TableRowEntries>
+          <TableRowEntry>
+            <TableColumnItems>
+              <TableColumnItem>
+                <PropertyName>RepositoryUrl</PropertyName>
+              </TableColumnItem>
+              <TableColumnItem>
+                <PropertyName>EnvironmentName</PropertyName>
+              </TableColumnItem>
+            </TableColumnItems>
+          </TableRowEntry>
+        </TableRowEntries>
+      </TableControl>
+    </View>
+  </ViewDefinitions>
+</Configuration>