Add timeouts for image resource

[raulgarbouzenitech]

Add defaults for create, delete and update in order to be able to override them when defining an image resource.

[m-ildefons]

Hi @raulgarbouzenitech , thanks for the contribution. The issue is well known to us and I'm currently working on adding timeout blocks to all resources that can use them. Check out my branch here.

[brandboat]

gentle ping @raulgarbouzenitech, I closed this pull request since the timeout block was added in https://github.com/harvester/terraform-provider-harvester/pull/97. If you have any other questions, feel free to ask. Thanks! 😃