Use make release for major/minor releases

[t-kikuc]

What this PR does / why we need it:

1. Uses make release instead of make release/init and make release/docs for major/minor releases.
   cf.

   pipecd/Makefile

   Lines 218 to 231 in 909fd76

   	.PHONY: release
   	release: release/init release/docs
   	.PHONY: release/init
   	release/init:
   	./hack/gen-release.sh $(version)
   	.PHONY: release/pick
   	release/pick:
   	./hack/cherry-pick.sh $(branch) $(pull_numbers)
   	.PHONY: release/docs
   	release/docs:
   	./hack/gen-release-docs.sh $(version)

2. Directly specifies to use make release/init for patch releases.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[Warashi]

👍🏻

[ffjlabo]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 22.83%. Comparing base (909fd76) to head (c4ac261).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5225   +/-   ##
=======================================
  Coverage   22.82%   22.83%           
=======================================
  Files         419      419           
  Lines       45304    45304           
=======================================
+ Hits        10340    10344    +4     
+ Misses      34169    34165    -4     
  Partials      795      795           

Flag	Coverage Δ
	22.83% <ø> (+<0.01%)	⬆️

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