fix: content-length header for broker token provision/switch endpoints

[soniqua]

What

• Adds Content-Length: 0 to empty POST requests for provision-token and switch-token endpoints

Why

• Without this (or without --data="") Akamai responds with 411 (no Content-Length header)

[gablaxian]

Is this not a breaking change? Or are you updating docs to reflect what was already there?

[soniqua]

@gablaxian the latter, this reflects current behaviour