feat: enable multiple IDE buttons in JetBrains

[matifali]

Add support for specifying a list of default IDEs to be displayed on the Workspace page. This allows users to see multiple IDE options simultaneously.

Closes #338

[!CAUTION] This introduces a few breaking changes in the module

1. The input default is now a list(string) instead of string, e.g.

   - default = "GO"
   + default = ["GO"]

2. All outputs are now of type list(string)
3. We hide the user choice coder_parameter when there are multiple items in default.

[phorcys420]

Works on my end, tested using the following snippet:

module "jetbrains_gateway" {
  count  = data.coder_workspace.me.start_count
  source = "git::https://github.com/coder/modules.git//jetbrains-gateway?ref=atif/multi-gateway"

  # JetBrains IDEs to make available for the user to select
  jetbrains_ides = ["IU", "PY", "WS", "PS", "RD", "CL", "GO", "RM"]
  default        = ["IU", "PY"]

  # Default folder to open when starting a JetBrains IDE
  folder = "/home/coder"

  agent_id   = coder_agent.dev[0].id
  agent_name = "dev"
  order      = 2
}

https://dev.coder.com/templates/coder/aws-linux/versions/strange_goldstine7