Replace static fields with single constants field in DevnetClient

[DelevoXDG]

Describe your changes

The xcodebuild docbuild command is the part of release CI workflow, which currently fails because of this command.
Apparently, the reason is using static values from DevnetClient, which fails because DevnetClient is internal, even though building and testing using XCode istelf works without issue despite that.

Since we probably want to keep DevnetClient and classes it uses internal, we could instead use enum DevnetClientConstants to hold the constants. We could then:

• Access DevnetClientConstants in methods inside DevnetClient methods when we need default values for arguments.
• Add constants field to easily access constants from DevnetClientProtocol from outside without needing to be aware of DevnetClientConstants.

Linked issues

Closes #108

Breaking changes

• This issue contains breaking changes

[drknzz]

lgtm