Fix web.external-prefix 404s and add web.prefix-header for bucket web UI. (thanos-io#1770)

* Add --web.prefix-header flag.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Update changelog.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Resolve conflicts with upstream.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Lint docs.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* More docs linting.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Remove extra flags.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Update changelog.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Lint docs.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>

* Final docs lint.

Signed-off-by: Christopher Manzi <chris.manzi@invitae.com>
Signed-off-by: Aleksey Sin <asin@ozon.ru>

Author: cmanzi

pkg/ui/bucket.go

@@ -20,7 +20,6 @@ type Bucket struct {
 	Blocks      template.JS
 	RefreshedAt time.Time
 	Err         error
-	flagsMap    map[string]string
 }
 
 func NewBucketUI(logger log.Logger, label string, flagsMap map[string]string) *Bucket {