Rewrite users service from ruby to rust

[mchf]

Problem

Current stable version of Agama is mixture of several languages and technologies. Users service was originally written in ruby. As we later on decided to prefer rust for various reasons, it makes sense to rewrite users service to rust.

Solution

This is initial PR for transition of users service to rust. Currently handles GET, PUT, PATCH /config and GET /proposal. However, no install action yet.

Testing

• Tested manually

[mchf]

Current state as a picture (curl -k -H @headers.txt -X GET $AGAMA_URL/api/v2/system):

once I publish even set config message there will also appear password (with values {type: hashed} or {type: plain, value: "whatever set by user"}, field next to name or may be slightly different - until it is set to stone, it can vary ;-)

[imobachgs]

The infrastructure of the service looks good, but the logic is wrong. Agama keeps the configuration for the first user (under the user key) and the root (using the root key). There is nothing like a list of users.

Additionally, it does not read the list of users from the underlying system. It just uses its own configuration.

Please, check User and root for further information about the format.

[mchf]

Set users config using query:

curl -X PATCH \
  -H @headers.txt \
  -H "Content-Type: application/json" \
  -d '{"update": {"product": { "id": "Tumbleweed" }, "users": { "users": { "user": { "fullName": "First User", "userName": "user", "password": "linux"}}}}}' \
  -k \
  $AGAMA_URL/api/v2/config

result:

Query for reading the config was:

curl -k -H @headers.txt -X GET $AGAMA_URL/api/v2/config

[mchf]

Schema fixed to work with:

curl -X PATCH \
  -H @headers.txt \
  -H "Content-Type: application/json" \
  -d '{"update": {"product": { "id": "Tumbleweed" }, "user": { "fullName": "First User", "userName": "user", "password": "linux"}}}' \
  -k \
  $AGAMA_URL/api/v2/config

Get query on config answers with:

{"product":{"id":"Tumbleweed"},"user":{"fullName":"First User","password":"linux","hashedPassword":false,"userName":"user"}}

[imobachgs]

Now it is looking good. But, please, update the description (now it only handles the configuration). We can work on the remaining stuff on a separate PR.

[mchf]

Rebased on top of current api-v2 branch

[coveralls]

coverage: 72.578%. remained the same
when pulling 5c863ff on users_service
into 11a30de on master.

[imobachgs]

I still some confusion with UserSettings and Config. Please, check the comments.

[imobachgs]

OK, we are almost there. Just minor comments. Otherwise it is looking good :-)