transactionWatch: Remove limits and stabilize to version 1

[lexnv]

This PR is a followup of the proposal from: https://github.com/paritytech/json-rpc-interface-spec/pull/150#pullrequestreview-1988787293

In this PR, the concept of limits is removed from the transactionWatch, as noted in: https://github.com/paritytech/json-rpc-interface-spec/pull/150.

• Servers can still return Transaction::Dropped if the node cannot keep up with the number of transactions (as per spec), however servers are not required to support a minimum of 4 subscriptions per client
• TransactionWatch is stabilized to version 1

cc @paritytech/subxt-team @tomaka

[tomaka]

I don't really understand the need to combine these two widely different things in a single PR?

[lexnv]

That makes sense, thanks for the review! 🙏

Have broken this down into:

• https://github.com/paritytech/json-rpc-interface-spec/pull/153
• https://github.com/paritytech/json-rpc-interface-spec/pull/154