Add x-e2ee-supported header to api example calls documentation

[myomv100]

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[artonge]

Thanks :)

[artonge]

/rebase

[artonge]

@myomv100 Looks like the CI is not picking up the jobs, can you rebase and push?

[artonge]

Closing in favor of https://github.com/nextcloud/end_to_end_encryption/pull/592 due to inactivity