Create resource group to apply memory setting for Isambard Instinct

[giordano]

@kaanolgu can you please check this works for you? If I remember correctly, we need to define the extra_resource so that it's applied in the configuration, but in this case we don't need (yet?) to define any custom variable, so I think an empty dictionary should work?

[giordano]

The reason why we haven't dealt with the memory as a proper resource so far is because it's complicated: it's a mixture of application-specific (memory requirements can vary a lot) and system-specific (I think for some schedulers it's the memory per CPU, in others it's the total memory), so it's really hard to come up with reasonable default values which work well in all situations.

[giordano]

@kaanolgu is it good to go now?

[kaanolgu]

@kaanolgu is it good to go now?

LGTM