Update the Technical Charter for Endusers-wg

[APM05]

Update the Endusers-wg technical charter: https://github.com/ossf/wg-endusers/blob/main/CHARTER.md

[afmarcum]

@torgo Still on track to have the initial edit for review next week? The readme has an objective, vision and scope that look updated if that helps.

[SecurityCRob]

+1

[jchester]

See #30 for a PR to set an adoption date.

[nealmcb]

It appears that the charter was approved and merged in February, as noted in #30. So this can be closed.