feat: add option to override placementStrategy for bootstrap command

[dateutli]

Description
Currently, bootstrap command only generates topic configs with a placement strategy of any. A better default value would be cross-rack as it aligns with what Kafka does when topics are created using its tooling.

In the given case that this placement strategy is not the desired one, I've updated the bootstrap command to add support for placement-strategy-overwrite flag. It defaults to the proposed cross-rack strategy if not provided but gives the opportunity to change it to any of the other strategies.

Testing
$ topicctl bootstrap topic-static --cluster-config="examples/local-cluster/cluster.yaml"

meta:
  cluster: local-cluster
  description: Bootstrapped via topicctl bootstrap
  environment: local-env
  labels: null
  name: topic-static
  region: local-region
spec:
  partitions: 10
  placement:
    strategy: cross-rack
  replicationFactor: 2
  retentionMinutes: 290

$ topicctl bootstrap topic-static --cluster-config="examples/local-cluster/cluster.yaml" --placement-strategy-overwrite="any"

meta:
  cluster: local-cluster
  description: Bootstrapped via topicctl bootstrap
  environment: local-env
  labels: null
  name: topic-static
  region: local-region
spec:
  partitions: 10
  placement:
    strategy: any
  replicationFactor: 2
  retentionMinutes: 290

[hhahn-tw]

Any reason not to use --placement-strategy rather than --placement-strategy-overwrite? The "-overwrite" part seems unnecessary.

[dateutli]

Any reason not to use --placement-strategy rather than --placement-strategy-overwrite? The "-overwrite" part seems unnecessary.

Thanks for the suggestion, I've updated the PR accordingly.