Fix several spelling mistakes

[christian-kreuzberger-dtx]

I just ran the Go Report Card Checker, and it found the following spelling mistakes that we need to fix:

Misspell Finds commonly misspelled English words

    keptn/shipyard-controller/api/event_test.go
    Line 953: warning: "corretly" is a misspelling of "correctly" (misspell)
    Line 1400: warning: "corretly" is a misspelling of "correctly" (misspell)

    keptn/api/handlers/metadata.go
    Line 24: warning: "pricipal" is a misspelling of "principal" (misspell)

    keptn/cli/cmd/auth.go
    Line 106: warning: "unsucessful" is a misspelling of "unsuccessful" (misspell)

    keptn/cli/cmd/install.go
    Line 59: warning: "derivate" is a misspelling of "derivative" (misspell)

    keptn/cli/cmd/upgrade.go
    Line 49: warning: "derivate" is a misspelling of "derivative" (misspell)

[christian-kreuzberger-dtx]

I'll not change the derivate part, as I believe it is correct.
https://diffsense.com/diff/derivate/derivative