Option to list all JSON output keys name

[ehsandeep]

Please describe your feature request:

A new option to list all the json output field keys name which can be further used with matchers / filters.

   -ldv, -list-dsl-variables  list json output field keys name that support dsl matcher/filter

httpx -ldv

timestamp
csp
domains
hash
body_md5
body_mmh3
body_sha256
body_simhash
header_md5
header_mmh3
header_sha256
header_simhash
port
url
input
location
scheme
webserver
content_type
method
host
path
time
a
words
lines
status_code
content_length
failed
body
header
request

Describe the use case of this feature:

New options which will support new dsl matcher/filter option using these keys name.

[forgedhallpass]

I think the -list-dsl flag name is confusing, because it doesn't refer to DSL function signatures as in other tools (nuclei and I think also proxify), but only shows the variable/constants that can be referenced from a DSL context. For this reason I would recommend renaming it to something like -list-dsl-variables or -list-dsl-attributes.