Add runtime chat script support for modem_chat module

[bjarki-trackunit]

Introduction

This PR makes it possible to construct modem chat scripts and modify them at runtime.

The problem

Some commands require runtime modification, including the response to said commands.

An example is this one for setting the 1PPS configuration of a GNSS modem:

send: "$PAIR752,3,200*DA"
receive: "$PAIR001,752,0*3B"

The parameters of the commands will change at runtime, so the chat script
needs to be modifiable at runtime.

The solution

Create a template script in RAM, that is modified before being run by the modem_chat instance.

/* Initialize script */
uint8_t match[32];
uint8_t request[32];

struct modem_chat_match match = {
	.match = match,
	.match_size = 0,
	.separators = NULL,
	.separators_size = 0,
	.wildcards = false,
	.partial = false,
	.callback = NULL,
};

struct modem_chat_script_chat script_chat = {
	.request = request,
	.request_size = 0;
	.response_matches = &match,
	.response_matches_size = 1,
	.timeout = 0,
};

struct modem_chat_script script = {
	.name = "config",
	.script_chats = &script_chat,
	.script_chats_size = 1,
	.abort_matches = NULL,
	.abort_matches_size = 0,
	.callback = NULL,
	.timeout = 1,
};

/* Modify script */
int ret = snprintk(match, sizeof(match), "$PAIR752,%u,%u*DA", 3, 200);
match.match_size = ret;
ret = snprintk(request, sizeof(request), "$PAIR001,%03u,0*3B", 752);
script_chat.request_size = ret;

/* Run script */
modem_chat_run_script(&chat, &stack_script);

Additional features

This PR also adds a function to synchronously run a chat script, and updates the naming scheme of the modem_chat module to clearly distinguish between the sync and async variant of the modem_chat_run_script() function, modem_chat_run_script_async().

[jukkar]

LGTM