hawkBit rest docs (management & DDI API) (#688)

* hawkBit REST docs.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fiy gitignore.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Add to website.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Switch to generated docs.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fix typos.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Review findings.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Otimizations.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Revert accidental checkin.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Add security link.

hawkbit-rest/hawkbit-rest-docs/src/main/errors/403.adoc

@@ -0,0 +1,3 @@
+| `403 Forbidden`
+| Insufficient permissions, entity is not allowed to be changed (i.e. read-only) or data volume restriction applies.
+| See <<error-body>>