feat: Add gRPC and REST definitions to A2A protocol specifications (#695)

- Requires adding a new `PushNotificationConfig.id` field to support
multiple push notification callbacks per task

---------

Co-authored-by: a2a-bot <[email protected]>
Co-authored-by: Holt Skinner <[email protected]>
Co-authored-by: Holt Skinner <[email protected]>

Author: 3 people

.github/actions/spelling/allow.txt

@@ -7,10 +7,12 @@ AClient
 ACo
 ADK
 AError
+AIP
 ARequest
 ASED
 ASGI
 AServer
+AService
 AStarlette
 Autogen
 CAs
@@ -19,12 +21,16 @@ Camry
 Cjava
 DDo
 DGT
+Dotnet
 EBFF
 EUR
 EUg
 FBT
+GAPI
+GAPIC
 GBP
 GVsb
+Gapic
 Genkit
 Ghw
 IFdvcmxk
@@ -45,7 +51,9 @@ Ollama
 PLE
 PLW
 PTH
+RPCs
 RUF
+SLAs
 SLF
 TMDB
 URLTo
@@ -87,6 +95,7 @@ cfe
 cls
 coc
 codegen
+codeowner
 crewai
 datamodel
 datapart
@@ -95,24 +104,31 @@ dcda
 dcfa
 dde
 direnv
+documentai
+dotnet
 efaab
 efbd
 embeddings
+envoyproxy
 evt
 excinfo
+faa
 fafd
 ffbb
 firewalls
 flightbook
 fsv
 fyi
+gapic
 gcp
 genai
 genkit
+genproto
 georoute
 gettickets
 gle
 googleai
+googleapi
 googleblog
 gpt
 gstatic
@@ -144,6 +160,7 @@ nlp
 notif
 noxfile
 npush
+objc
 octicons
 ollama
 oneof
@@ -176,6 +193,7 @@ tok
 tracestate
 ugc
 utm
+versioned
 vnd
 voa
 webpage