Support function flags in script EVAL via shebang header (#10126)

In #10025 we added a mechanism for flagging certain properties for Redis Functions.
This lead us to think we'd like to "port" this mechanism to Redis Scripts (`EVAL`) as well. 

One good reason for this, other than the added functionality is because it addresses the
poor behavior we currently have in `EVAL` in case the script performs a (non DENY_OOM) write operation
during OOM state. See #8478 (And a previous attempt to handle it via #10093) for details.
Note that in Redis Functions **all** write operations (including DEL) will return an error during OOM state
unless the function is flagged as `allow-oom` in which case no OOM checking is performed at all.

This PR:
- Enables setting `EVAL` (and `SCRIPT LOAD`) script flags as defined in #10025.
- Provides a syntactical framework via [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)) for
  additional script annotations and even engine selection (instead of just lua) for scripts.
- Provides backwards compatibility so scripts without the new annotations will behave as they did before.
- Appropriate tests.
- Changes `EVAL[SHA]/_RO` to be flagged as `STALE` commands. This makes it possible to flag individual
  scripts as `allow-stale` or not flag them as such. In backwards compatibility mode these commands will
  return the `MASTERDOWN` error as before.
- Changes `SCRIPT LOAD` to be flagged as a `STALE` command. This is mainly to make it logically
  compatible with the change to `EVAL` in the previous point. It enables loading a script on a stale server
  which is technically okay it doesn't relate directly to the server's dataset. Running the script does, but that
  won't work unless the script is explicitly marked as `allow-stale`.

Note that even though the LUA syntax doesn't support hash tag comments `.lua` files do support a shebang
tag on the top so they can be executed on Unix systems like any shell script. LUA's `luaL_loadfile` handles
this as part of the LUA library. In the case of `luaL_loadbuffer`, which is what Redis uses, I needed to fix the
input script in case of a shebang manually. I did this the same way `luaL_loadfile` does, by replacing the
first line with a single line feed character.

5 files changed, 10 insertions, 5 deletions

diff --git a/src/commands/eval.json b/src/commands/eval.json
index cbd79bc87..673722cf5 100644
--- a/src/commands/eval.json
+++ b/src/commands/eval.json
@@ -11,7 +11,8 @@
             "NOSCRIPT",
             "SKIP_MONITOR",
             "MAY_REPLICATE",
-            "NO_MANDATORY_KEYS"
+            "NO_MANDATORY_KEYS",
+            "STALE"
         ],
         "acl_categories": [
             "SCRIPTING"
diff --git a/src/commands/eval_ro.json b/src/commands/eval_ro.json
index 75e717b3e..58b744591 100644
--- a/src/commands/eval_ro.json
+++ b/src/commands/eval_ro.json
@@ -10,7 +10,8 @@
         "command_flags": [
             "NOSCRIPT",
             "SKIP_MONITOR",
-            "NO_MANDATORY_KEYS"
+            "NO_MANDATORY_KEYS",
+            "STALE"
         ],
         "acl_categories": [
             "SCRIPTING"
diff --git a/src/commands/evalsha.json b/src/commands/evalsha.json
index 50646858d..9b68b87f1 100644
--- a/src/commands/evalsha.json
+++ b/src/commands/evalsha.json
@@ -11,7 +11,8 @@
             "NOSCRIPT",
             "SKIP_MONITOR",
             "MAY_REPLICATE",
-            "NO_MANDATORY_KEYS"
+            "NO_MANDATORY_KEYS",
+            "STALE"
         ],
         "acl_categories": [
             "SCRIPTING"
diff --git a/src/commands/evalsha_ro.json b/src/commands/evalsha_ro.json
index ab47e4773..d876c5d76 100644
--- a/src/commands/evalsha_ro.json
+++ b/src/commands/evalsha_ro.json
@@ -10,7 +10,8 @@
         "command_flags": [
             "NOSCRIPT",
             "SKIP_MONITOR",
-            "NO_MANDATORY_KEYS"
+            "NO_MANDATORY_KEYS",
+            "STALE"
         ],
         "acl_categories": [
             "SCRIPTING"
diff --git a/src/commands/script-load.json b/src/commands/script-load.json
index 0a19c9193..b0b4e67e5 100644
--- a/src/commands/script-load.json
+++ b/src/commands/script-load.json
@@ -8,7 +8,8 @@
         "container": "SCRIPT",
         "function": "scriptCommand",
         "command_flags": [
-            "NOSCRIPT"
+            "NOSCRIPT",
+            "STALE"
         ],
         "acl_categories": [
             "SCRIPTING"