Enable strict typing in ./server

[leafty]

See for example:

error: Cannot read properties of undefined (reading 'toLowerCase') {"service":"renku-ui-server"}
info: Sending error to sentry {"service":"renku-ui-server"}
This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason:
TypeError: Cannot read properties of undefined (reading 'toLowerCase')
    at Authenticator.<anonymous> (/app/dist/authentication/authenticator.js:64:18)
    at Generator.next (<anonymous>)
    at /app/dist/authentication/authenticator.js:25:71
    at new Promise (<anonymous>)
    at __awaiter (/app/dist/authentication/authenticator.js:21:12)
    at Authenticator.authenticate (/app/dist/authentication/authenticator.js:58:16)
    at /app/dist/authentication/authenticator.js:104:34
    at Generator.next (<anonymous>)
    at /app/dist/authentication/authenticator.js:25:71
    at new Promise (<anonymous>)

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