PWX-28113: Fix ListMembers API and add a new RemoveMemberByID API.

[adityadani]

What this PR does / why we need it: ListMembers API

• The ListMembers API used to return a map[string]*MemberInfo. The key to this map was the name of a member.
• However when there is unstarted etcd member, the name of the member is set to empty.
• Changed the API to return a map[uint64]*MemberInfo, where the key is a unique ID which is always set (even for unstarted members).
• Also added HasStarted and Name fields to MemberInfo for easy lookup.

RemoveMemberByID API

• Introduced a new API to remove members based on their IDs.

UTs

• Fixed existing UTs to handle the new API.
• Added tests for RemoveMemberByID API.
• Added more checks to existing UTs.

Which issue(s) this PR fixes (optional) Closes #

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