Group member label support

[Berglund]

I had a use-case for the new label (and emoji) feature in groups, and noted that signal-cli had support (AsamK/signal-cli@27a722d) but not signal-cli-rest-api.

If unaware of this functionality, it allows you to set a label for yourself in a group that's then visible for others:

This PR has three commits;

f07c587 adds support for setting the label via PUT /v1/groups/<number>/<group id> with member_label and member_label_emoji.

0938262 exposes the labels set in various groups on GET /v1/groups/<number>.

fc9a90c updates the public request interface based on review feedback, using the nested structure {"member_label": {"name": "<label>", "emoji": "<emoji>"}}.

[bbernhard]

Thanks a lot for the PR!

In general I think the PR is fine. What I am unsure though is, the structure of the public interface. I think I'd prefer some like:

MemberLabel struct {
   Name      *string         `json:"name,omitempty"
   Emoji      *string         `json:"emoji,omitempty"`
} `json:"member_label,omitempty"`

What do you think?

[Berglund]

Hey! So sorry for the late response. Parental leave is taking the time it requires 😅

I like your suggestion! Took a stab at it in fc9a90c - see what you think.