Hcl2 input variables, local variables and functions

[azr]

This draft PR introduces basic variables handling; similarly to what currently works in Packer, for example:

variables {
    foo = "value ${1 + 2}"
    my_secret = "bar"
    image_name = "foo-image"
}

variable "image_id" {
  type = string
  default = lower("image-id-DEFAULT")
}

variable "availability_zone_names" {
  type    = list(string)
  default = ["a", "b", "c"]
}

locals {
  feefoo = "${var.foo}_${var.image_id}"
}

// var.foo == "value 3"
// var.feefoo == "value 3_image-id-default"

• Adding numbers just worked out of the box.
• open a PR to move functions from terraform (docs), over to go-cty: Import functions from Terraform zclconf/go-cty#37 and Import functions from Terraform go-cty-funcs#4
• parse sensitive vars
• setting vars from varfiles
• setting vars from the command line
• setting vars from the env ?
• local vars ?
• introduce vars that aren't just strings ? link
• bring test coverage up to 70% ( + making sure variables are well tested )
• add docs for variables/locals
• updated index of docs
• pass sensible vars to core
• make file functions work with directory
• document the hcl2template package better

Closes #6988
Closes #8681

EDIT: The following functions have been added:
abs, abspath, basename, base64decode, base64encode, bcrypt, can, ceil, chomp, chunklist, cidrhost, cidrnetmask, cidrsubnet, cidrsubnets, coalesce, coalescelist, compact, concat, contains, convert, csvdecode, dirname, distinct, element, file, fileexists, fileset, flatten, floor, format, formatdate, formatlist, indent, index, join, jsondecode, jsonencode, keys, length, log, lookup, lower, max, md5, merge, min, parseint, pathexpand, pow, range, reverse, rsadecrypt, setintersection, setproduct, setunion, sha1, sha256, sha512, signum, slice, sort, split, strrev, substr, timestamp, timeadd, title, trim, trimprefix, trimspace, trimsuffix, try, upper, urlencode, uuidv4, uuidv5, values, yamldecode, yamlencode, zipmap.

[azr]

Okay we decided to go on with that one ! The sensible var obfuscating is going to come up in another PR ! 🙂

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.