Phase out environment variables prefixed DRONE_, use WOODPECKER_

[marians]

Currently (as of v0.13.0), every environment variable for configuring woodpecker seems to come in two flavours: One prefixed DRONE_ and one prefixed WOODPECKER_.

The coexistence of these two versions of variables with identical meaning makes documentation, help text, and error messages hard to read (see my PR #208 for an example).

To improve the user experience, I recommend to make a decision regarding when to drop the DRONE_ spelling and communicate that decision clearly.

Since woodpecker is still in the v0.x.x major version realm, I would argue such a change could happen with any minor version bump.

[laszlocph]

Let's do it.

It has been a maintenance pain.

The main reason for keeping both prefixes is to ease the migration from Drone. While I've seen users migrating from 0.8, many of the new users are either coming from Drone 1.X, or new to Woodpecker completely.

Let's drop DRONE_* and communicate the breaking change in the release notes.

[marians]

How about using the occasion for these additional clean-ups?

• Remove DATABASE_DRIVER in favour of WOODPECKER_DATABASE_DRIVER
• Remove DATABASE_CONFIG in favour of WOODPECKER_DATABASE_DATASOURCE
• Remove WOODPECKER_HOSTin favour of WOODPECKER_SERVER_HOST
• Remove WOODPECKER_SECRET in favour of WOODPECKER_AGENT_SECRET

IMO it would help to remove the guesswork and make the code more maintainable.

[marians]

... and rename XDG_CACHE_HOME to WOODPECKER_LETS_ENCRYPT_PATH

[tboerger]

It's best practice for many projects to prefix the env variables by the project name, so let's use WOODPECKER_.

The xdg env variable should keep the name as it is.

[tboerger]

XDG_CACHE_HOME is a standard env variable name from freedesktop and it's only the base path where the let's encrypt certificates are stored.