Rename discriminator to waf everywhere (closes #312)

The command is now `sww waf`, and the package is `internal/waf`. Types,
functions, files, tests, comments, docs, the Dockerfile, the runit
script, `script/`, compose examples, the log field `waf_line` and the
`X-From-Waf` test header follow. No behaviour changes, and no setting
changes name: rproxy already finds the waf through `SWRP_WAF_BACKEND`.

Done with one `sed -i` (Discriminator and DISCRIMINATOR to WAF,
discriminator to waf) over the files `git grep -i discriminator`
listed, as sneak allowed for this rename, then `git mv` for the
package and files. By hand afterwards: the header's spelling, which
the linter requires, and the padding after `waf` in `sww`'s usage
text.

Model: opus-5-5

docs/state-files.md

@@ -7,7 +7,7 @@ a top-level `version` of 1.
 ## `bans.json`
 
 Active and past bans: every ban an admin made, and up to `SWW_MAX_BANS` of those
-`discriminator` made. Per entry:
+`waf` made. Per entry:
 
 - `netblock`, `start` and `expires` (`null` for a permanent ban);
 - `cause`: `attack`, `limit`, `admin` or `crowdsec`;