Add global kv

[adamcrossland]

This change adds a global kv store that can be accessed by multiple
functions.

To make this possible, this change adds three new functions to the kv
interface: getGlobal, setGlobal and deleteGlobal. These functions map
the behavior of get, set, and delete.

For example, let's say that I want to have an HTTP handler function
that increments a counter each time that it is called:

function handler(ctx, event)
    local count = kv.getGlobal("visitCounter") or 0
    count = count + 1
    kv.setGlobal("visitCounter", count)

    return {
        statusCode = 200,
        headers = { ["Content-Type"] = "application/json" },
        body = json.encode({
            message = "Visit count = " .. count
        })
    }
end

I also want to have a function that runs every minute to email a
report of the number of times that the first function has been
called:

function handler(ctx, event)
    -- Get data to report
    local count = kv.getGlobal("visitCounter") or 0

    -- Send email via Resend
    local result, err = email.send({
        from = "reports@fakeurl.dev",
        to = "reportreceivingperson@gmail.com",
        subject = "Current visit counter value",
        html = "<p>Current visit counter value is " .. count .. "</p>",
    })

    if err then
        log.error("Email error: " .. err)
        return {
            statusCode = 500,
            headers = { ["Content-Type"] = "application/json" },
            body = json.encode({ error = err })
        }
    end

    log.info("Email sent: " .. result.id)

    return {
        statusCode = 200,
        headers = { ["Content-Type"] = "application/json" },
        body = json.encode({
            success = true,
            email_id = result.id
        })
    }
end

The kv.getGlobal, kv.setGlobal and kv.deleteGlobal functions allow access to a kv store that is shared by all function.

[dimiro1]

Thank you!