Autocomplete HTTP header keys.

[VictorioBerra]

Is your feature request related to a problem? Please describe.
I forget the names of HTTP headers.

Describe the solution you'd like
When typing "Accept", after I type "Ac..." show me a list of HTTP headers that start with "Ac"

There is a big list of common headers we could pre-fill a list in code to autocomplete from easily.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.