Introduce a pool builder to replace static pool methods

[vietj]

Goals

• current design with static methods has limited extensibility
  • SqlConnectOptions do not extend anymore NetClientOptions and user should be able to configure it which would clutter the current static methods
• go away from Pool sub types as they don't declare any methods

Deprecations

For removal in a subsequent PR

• deprecates Pool subclasses, e.g PgPool
• deprecate Pool#connectHandler and Pool#connectionProvider

Proposal

A builder class takes an driver instance and build the client according to its state.

Pool pool;

// Build pool with default settings
pool = PgBuilder.pool().using(vertx).build();

// With specific pool settings
pool = PgBuilder
   .pool()
   .connectingTo(new PgConnectOptions().setHost(host).setUsername(username).setPassword(password))
   .using(vertx)
   .build();

// With specific pool settings
pool = PgBuilder
   .pool()
   .with(new PoolOptions().setMaxSize(5))
   .using(vertx)
   .build();

// We should also be able to build pipelined clients when the database supports it
SqlClient client = PgBuilder
   .client()
   .connectingTo(new PgConnectOptions().setHost(host).setUsername(username).setPassword(password))
   .using(vertx)
   .build();

An alternative pattern for the builder API is also provided:

Pool pool = PgBuilder
   .pool(builder -> builder.
      .connectingTo(new PgConnectOptions().setHost(host).setUsername(username).setPassword(password))
      .using(vertx));