docs: add xapp section

[kuredev]

Summary

I added an explanation about saving a certain environment variable to the Japanese documentation since it was mentioned in the English documentation but not in the Japanese one.

en

ja

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.49%. Comparing base (7020a2e) to head (2662aa3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2339   +/-   ##
=======================================
  Coverage   92.49%   92.49%           
=======================================
  Files          36       36           
  Lines        7472     7472           
  Branches      651      651           
=======================================
  Hits         6911     6911           
  Misses        553      553           
  Partials        8        8           

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[seratch]

Thank you so much for taking the time to improve the docuement! May I ask you to work on the HTTP tab too?

[seratch]

If you don't mind, can I ask you to work on this too?

[kuredev]

Sorry, I misunderstood the meaning of "Carry on!"

It seems that saving the xapp token is unnecessary in HTTP mode, so I think it's fine to proceed without setting it.

Therefore, I fixed it to mean "please proceed as is." How does this look? 13a72bf

[seratch]

LGTM; Thank you so much for taking the time!