[ObjC] Upgrade podspec xx.deployment_target (grpc#33091)

Upgrade apple platform deployment_target versions to fix the cocoapods
push of BoringSSL-GRPC about the following error:
```
ld: file not found: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/arc/libarclite_macosx.a
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```
ref: https://developer.apple.com/forums/thread/725300

This also aligns with the versions required by
[protobuf](protocolbuffers/protobuf#10652)

```
ios.deployment_target = '10.0'
osx.deployment_target = '10.12'
tvos.deployment_target = '12.0'
watchos.deployment_target = '6.0'
```

Author: HannahShiSFB

examples/cpp/helloworld/cocoapods/Podfile

@@ -1,5 +1,5 @@
 source 'https://github.com/CocoaPods/Specs.git'
-platform :ios, '8.0'
+platform :ios, '10.0'
 
 install! 'cocoapods', :deterministic_uuids => false
 

examples/objective-c/auth_sample/AuthTestService.podspec

@@ -7,8 +7,8 @@ Pod::Spec.new do |s|
   s.summary = "AuthTestService example"
   s.source = { :git => 'https://github.com/grpc/grpc.git' }
 
-  s.ios.deployment_target = "9.0"
-  s.osx.deployment_target = "10.10"
+  s.ios.deployment_target = "10.0"
+  s.osx.deployment_target = "10.12"
 
   # Base directory where the .proto files are.
   src = "../../protos"

examples/objective-c/auth_sample/Podfile

@@ -1,5 +1,5 @@
 source 'https://github.com/CocoaPods/Specs.git'
-platform :ios, '9.0'
+platform :ios, '10.0'
 
 install! 'cocoapods', :deterministic_uuids => false
 

examples/objective-c/helloworld/HelloWorld.podspec

@@ -7,8 +7,8 @@ Pod::Spec.new do |s|
   s.summary = "HelloWorld example"
   s.source = { :git => 'https://github.com/grpc/grpc.git' }
 
-  s.ios.deployment_target = "9.0"
-  s.osx.deployment_target = "10.10"
+  s.ios.deployment_target = "10.0"
+  s.osx.deployment_target = "10.12"
 
   # Base directory where the .proto files are.
   src = "../../protos"

examples/objective-c/helloworld/Podfile

@@ -1,5 +1,5 @@
 source 'https://github.com/CocoaPods/Specs.git'
-platform :ios, '9.0'
+platform :ios, '10.0'
 
 install! 'cocoapods', :deterministic_uuids => false
 

examples/objective-c/helloworld_macos/HelloWorld.podspec

@@ -7,8 +7,8 @@ Pod::Spec.new do |s|
   s.summary = "HelloWorld example"
   s.source = { :git => 'https://github.com/grpc/grpc.git' }
 
-  s.ios.deployment_target = "9.0"
-  s.osx.deployment_target = "10.10"
+  s.ios.deployment_target = "10.0"
+  s.osx.deployment_target = "10.12"
 
   # Base directory where the .proto files are.
   src = "../../protos"

examples/objective-c/helloworld_macos/Podfile

@@ -1,5 +1,5 @@
 source 'https://github.com/CocoaPods/Specs.git'
-platform :macos, '10.10'
+platform :macos, '10.12'
 
 install! 'cocoapods', :deterministic_uuids => false
 

examples/objective-c/route_guide/Podfile

@@ -1,5 +1,5 @@
 source 'https://github.com/CocoaPods/Specs.git'
-platform :ios, '9.0'
+platform :ios, '10.0'
 
 install! 'cocoapods', :deterministic_uuids => false
 

examples/objective-c/route_guide/RouteGuide.podspec

@@ -7,8 +7,8 @@ Pod::Spec.new do |s|
   s.summary = "RouteGuide example"
   s.source = { :git => 'https://github.com/grpc/grpc.git' }
 
-  s.ios.deployment_target = "9.0"
-  s.osx.deployment_target = "10.10"
+  s.ios.deployment_target = "10.0"
+  s.osx.deployment_target = "10.12"
 
   # Base directory where the .proto files are.
   src = "../../protos"