feat(module/bootstrap): add possibility to upload whole folder structure

[FoSix]

Description

Introduce changes suggested by @ntwrkguru in #254

Motivation and Context

Since #255 was created the code base had a huge refactor, hence the original PR could not be merged. This one introduces the originally suggested changes but in the new code base. This is basically a backport from google repository

Closes #255

How Has This Been Tested?

This can be tested with the following code:

# Create or source the Resource Group.
resource "azurerm_resource_group" "this" {
  name     = "bootstrap-test"
  location = "North Europe"
}

module "bootstrap_share" {
  source = "../../modules/bootstrap"

  create_storage_account = true
  name                   = "fgkjlskdjflkajsdlfk"
  resource_group_name    = azurerm_resource_group.this.name
  location               = azurerm_resource_group.this.location
  storage_share_name     = "ashare"
  files                  = { "files/init-cfg.txt" = "config/init-cfg.txt" }
  bootstrap_files_dir    = "bootstrap_schema"
  storage_acl            = false
}

where bootstrap_schema can have the following structure:

bootstrap_schema
├── config
│   └── init-cfg.txt
├── content
├── license
│   └── licence.file
├── plugins
│   └── plugins.file
└── software

Screenshots (if appropriate)

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes if appropriate.
• All new and existing tests passed.