Ability to define multiple subnets in SUBNET_FILTER

[zipiju]

It currently looks like you can only define single allowed subnet in SUBNET_FILTER, such as SUBNET_FILTER=spark.
Trying to do SUBNET_FILTER=spark,arweave causes the node to run no subnets (tried with --experimental flag, where while omitting the SUBNET_FILTER the node runs all currently available subnets - three at the moment).
The reason to run node in this configuration might for example be RAM constraints, where you would be able to run two subnets, but running three would cause an OOM condition.
Would it be possible to modify the code so it would parse for example comma separated SUBNET_FILTER, to allow users to define which specific subnets to run?
Thank you.

[bajtos]

Here is the relevant code:

node/lib/zinnia.js

Lines 87 to 88 in 8bcce7e

	const matchesSubnetFilter = (subnet) =>
	SUBNET_FILTER === '' || subnet === SUBNET_FILTER

Would you like to contribute the change yourself and submit a pull request?

[zipiju]

Sure, this will hopefully do #719