Add --wait flag to databases migrate command

[loosla]

What is the problem this feature would solve? Please describe. doctl aims to be useful in scripting. One way it does this is by providing a --wait flag for long running, async operations to block until they are complete rather than making the user implement polling in their own script. Some examples include:

• doctl database create --wait
• doctl compute droplet create --wait
• doctl kubernetes cluster create --wait
• doctl apps create --wait

Currently the doctl databases migrate command does not have a --wait flag.

Describe the solution you'd like Add a --wait flag to the doctl databases migrate command. It should poll the /v2/databases/$DATABASE_ID/migrate, blocking until the database cluster's status attribute moves from migrating to online.

Additional context Following the code path starting here demonstrates how doctl database create's --wait flag is implemented:

https://github.com/digitalocean/doctl/blob/de1918ad1ee4b1e523c335fa9254e85d415d18aa/commands/apps.go#L282

[shashank-priyadarshi]

@loosla can I please take this up?

[loosla]

@shashank-priyadarshi We would certainly value your input. :+1: