Change config.chunks indexes on upgrade/downgrade

On FCV upgrade to 5.0, make changes to the indexes for config.chunks as to:

• Create uuid-based indexes (uuid_1_min_1, uuid_1_shard_1_min_1, uuid_1_lastmod_1)
• Drop nss-based indexes (ns_1_min_1, ns_1_shard_1_min_1, ns_1_lastmod_1)

On FCV downgrade from 5.0 to earlier:

• Create the nss-based indexes
• Drop the uuid-based indexes