Refactor of ClientOptions

[ikurek]

This is a part of #61, including changes only for ClientOptions and AuthOptions, without moving the fields as private. Main changes:

• Updated constructor of AuthOptions and ClientOptions to use named parameters
• Deprecated fromKey methods, since the object can be now created with constructor invocation
• Refactored all places where ClientOptions was created with public parameter setters

Although this PR is fairly large, most of the changes were done in integration testing, and none of the changes are breaking in any way - users should be able to migrate without any issues. Moving the variables as private is a breaking change, so I decided to implement this later, in a separate PR, to give users some more time to adopt these changes before we deprecate the public fields

[KacperKluka]

Overall everything looks good but I think that one thing is missing - update in the README and Ably docs 😉 Since we've deprecated the fromKey I believe we shouldn't suggest it in our usage guides.

I took a quick look and found at least 3 places (but there may be more) in which we're using the deprecated fromKey approach:

• project README (let's update it as a part of this PR)
• Ably quickstart guide (probably we should inform the docs team about it, what's the best way to do this @QuintinWillison ? 🤔 )
• plugin details on pub.dev (probably this is taken from the README and will be updated automatically with the next release, right?)

[ikurek]

Overall everything looks good but I think that one thing is missing - update in the README and Ably docs 😉 Since we've deprecated the fromKey I believe we shouldn't suggest it in our usage guides.

Good catch! I forgot about README, I'm going to update it in a while, but I'm not sure about the docs and quickstart guide - I've checked the spec before this refactor and there's no reference to fromKey in the spec itself, so I'm not sure if we should include it in quickstart guide?

You're correct with pub.dev descriptions, it's generated from the readme file 🙂

I've fixed these references in 8a7666d

[KacperKluka]

LGTM now, thanks 😉 The only thing left is the fromKey() reference in the Ably docs but this is outside of this PR scope, as the change should probably be made after this PR is released in a new ably-flutter version 🤔

[QuintinWillison]

Looks good to me, albeit admitting I have skim read much of the contents.