Implement AddApplication rpc for external api

[nghialv]

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]

/cc @khanhtc1202

[pipecd-bot]

Code coverage for golang is 33.97%. This pull request increases coverage by 0.01%.

File	Function	Base	Head	Diff
pkg/app/api/grpcapi/api.go	requireAPIKey	--	100.00%	+100.00%
pkg/app/api/grpcapi/utils.go	getPiped	--	57.14%	+57.14%
pkg/app/api/grpcapi/utils.go	makeGitPath	--	0.00%	+0.00%
pkg/rpc/rpcauth/interceptor.go	ContextWithAPIKey	--	100.00%	+100.00%
pkg/app/api/grpcapi/api.go	API.AddApplication	0.00%	0.00%	+0.00%
pkg/app/api/grpcapi/api.go	API.SyncApplication	0.00%	0.00%	+0.00%
pkg/app/api/grpcapi/web_api.go	WebAPI.AddApplication	0.00%	0.00%	+0.00%
pkg/app/piped/logpersister/stagelogpersister.go	stageLogPersister.flushFromLastCheckpoint	61.11%	50.00%	-11.11%
pkg/rpc/rpcauth/interceptor.go	ExtractAPIKey	75.00%	100.00%	+25.00%
pkg/app/api/grpcapi/web_api.go	WebAPI.getPiped	57.14%	--	-57.14%
pkg/app/api/grpcapi/web_api.go	WebAPI.makeGitPath	0.00%	--	+-0.00%

[khanhtc1202]

/approve

[pipecd-bot]

This pull request is APPROVED by khanhtc1202.

Approvers can cancel the approval by writing /approve cancel in a comment. Any additional commits also will change this pull request to be not-approved.