Update Alloy variables to use the grafana_alloy_ namespace so they are unique

[Aethylred]

This should address #206 and #194

This PR should make sure the Alloy variables are unique and won't clash with other variables (like version) used elsewhere in playbooks.

It also moves the binary and working directory out of /etc where RHEL and SELinux get upset about.

[CLAassistant]

All committers have signed the CLA.

[v-zhuravlev]

LGTM.

[gardar]

Please prefix the variables with alloy_ rather than grafana_alloy_ to comply with the ansible-lint rule var-naming[no-role-prefix] as the role name is alloy and not grafana_alloy

[ishanjainn]

Hey @Aethylred Yeah would prefer to use alloy_ instead of grafana_alloy_

[Aethylred]

Switched to alloy_ as requested, though I suppose the code is ahead of this now.

Apologies about the delay, with the Alloy setup being immature, we switched to using the standard Grafana setup. Will be skipping Grafana Agent & Flow and waiting for Alloy.

[ishanjainn]

#228

BOth of the PRs seem to achive the same thing, @Aethylred Lemme know if the other PR loogs good to you aswell and we can use that or the other way around?

[Aethylred]

Looking at #228 and it looks good, I'd consider it a duplicate, but whichever crosses the line first is fine by me