Update Hugo version for the site

[ffjlabo]

What happened

The Hugo version is a little bit old. So it would be nice to update it.
Also, if possible, update the theme Docsy version.

TODO

• Update config for github actions
• Update docsy version (if possible)

How to reproduce it:

Environment:

• piped version:
• control-plane version:
• Others:

[t-kikuc]

Update docsy version (if possible)

although we have make update/docsy, I'm not sure it works well...

pipecd/Makefile

Lines 190 to 193 in 739ccb0

	.PHONY: update/docsy
	update/docsy:
	rm -rf docs/themes/docsy
	git clone --recurse-submodules --depth 1 https://github.com/google/docsy.git docs/themes/docsy