This mod adds option to authenticate user using HTTP header set by
reverse proxy. It forwards specified HTTP header with authenticated
username in requests to Gitea.

Requirements:

* Gitea must be configured for reverse proxy authentication and
  must accept HTTP header auth in API calls (Gitea fix IB#1107572).

* Woodpecker must use its external host address in status URL-s
  sent to Gitea (Woodpecker fix IB#1107596).

To enable set the following variables in woodpecker server
environment (woodpecker running behind reverse proxy):

* internal woodpecker server URL, i.e.:

  WOODPECKER_HOST_INTERNAL=http://192.168.1.100:8000

* enable reverse proxy auth in woodpecker and forwarding auth
  header to gitea:

  WOODPECKER_GITEA_REV_PROXY_AUTH=true

* set name of header with authenticated username (set by
  reverse proxy), i.e.:

  WOODPECKER_GITEA_REV_PROXY_AUTH_HEADER=X-Forward-Username

Author-Change-Id: IB#1107569

Missing information about file changes added.

Fixes: 66d8ff7
Author-Change-Id: IB#1107569

Company name fixed.

Fixes: 3888838
Author-Change-Id: IB#1107569