feat: optional pending state for ContextCommand (#687)

## Problem
In large workspaces, indexing can take a long time with no indication of
status
## Solution
An optional pending flag is added to ContextCommand definition type.
This allows a pending state to be indicated before the Context Command
is sent to the client. The ui can then interpret this pending flag to
grey out and disable the context command
Should be merged before aws/mynah-ui#421 and
aws/language-servers#2060
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**This pr is a replacement of the
#652

## License

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

---------

Co-authored-by: Conor Stewart <[email protected]>
Co-authored-by: constewart9 <[email protected]>
Co-authored-by: manodnyab <[email protected]>

Author: 3 people

types/chat.ts

@@ -462,6 +462,7 @@ export interface ContextCommand extends QuickActionCommand {
     label?: 'file' | 'folder' | 'code' | 'image'
     children?: ContextCommandGroup[]
     content?: Uint8Array
+    disabledText?: string
 }
 
 export interface ContextCommandParams {