[event-hubs][service-bus] re-export RetryMode enum from core-amqp

[chradek]

The clients from @azure/event-hubs and @azure/service-bus accept RetryOptions as defined in @azure/core-amqp.

One of the fields in RetryOptions, mode, is an enum called RetryMode that allows users to choose a fixed or exponential retry strategy.

Currently RetryMode is not re-exported by the @azure/event-hubs and @azure/service-bus packages, so to specify a mode, a user would need to import the RetryMode enum from @azure/core-amqp.

Instead, we should re-export RetryMode so users don't need to depend directly on our core-amqp package.

Related to #12587

[snuffykl]

@chradek Curious is there a way for us(client) to specify this retry for @azure/service-bus package as a SB Topic sender when calling function sendbatch ?

[HarshaNalluru]

@snuffykl
You can specify the retryOptions at the client level such as below.

    new ServiceBusClient("<connection-string>", {
      retryOptions: { mode: RetryMode.Exponential, maxRetries: 5, timeoutInMs: 3000 }
    });