Add platform provider to application, deployment and piped model

[khanhtc1202]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[nghialv]

The CI job does not pass.

[pipecd-bot]

The following ISSUES will be created once got merged. If you want me to skip creating the issue, you can use /todo skip command.

Details

---

1. Add validation for this field.

pipecd/pkg/model/application.pb.go

Lines 115 to 118 in e4f4816

	// TODO: Add validation for this field.
	PlatformProvider string `protobuf:"bytes,15,opt,name=platform_provider,json=platformProvider,proto3" json:"platform_provider,omitempty"`
	// Additional description about application.
	Description string `protobuf:"bytes,9,opt,name=description,proto3" json:"description,omitempty"`

This was created by todo plugin since "TODO:" was found in e4f4816 when #3756 was merged. cc: @khanhtc1202.

---

2. Add validation for this field.

pipecd/pkg/model/application.proto

Lines 44 to 47 in e4f4816

	// TODO: Add validation for this field.
	string platform_provider = 15;
	// Additional description about application.
	string description = 9;

This was created by todo plugin since "TODO:" was found in e4f4816 when #3756 was merged. cc: @khanhtc1202.

[khanhtc1202]

/todo skip

[nghialv]

👍

[knanao]

Here you go!