Refactor the add application form

[cakecatz]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[pipecd-bot]

Code coverage for golang is 23.95%. This pull request does not change code coverage.

[pipecd-bot]

Code coverage for javascript is 67.80%. This pull request increases coverage by 1.56%.

File	Base	Head	Diff
src/components/add-application-form.tsx	--	92.45%	+92.45%
src/constants/ui-text.ts	--	100.00%	+100.00%
src/api/applications.ts	21.43%	21.05%	-0.38%
src/modules/pipeds.ts	50.00%	53.57%	+3.57%

[nghialv]

/approve

[pipecd-bot]

This pull request is APPROVED by nghialv.

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