This commit adds the ability to enable / disable relocations
on an entire cluster or on individual indices for either:
* `primaries` - only primaries can rebalance
* `replica` - only replicas can rebalance
* `all` - everything can rebalance (default)
* `none` - all rebalances are disabled
similar to the allocation enable / disable functionality.
Relates to #7288
This documentation was dangerous because it felt like it was possible to gain
substantial performance by just switching the codec of the index.
However, non-default codecs are dangerous to use since they are not supported
in terms of backward compatibility, and most improvements that they bring have
been folded into the default codec anyway (for example, the default codec
"pulses" postings lists that contain a single document).
Previously if the user provided a non-conforming string, it would blow up with
`java.lang.StringIndexOutOfBoundsException: String index out of range: -1`
which is not a *helpful* error message.
Also updated the documentation to make the possible setting values more clear.
Close#5752
`allocation.disable_new_allocation`, `allocation.disable_allocation`, `allocation.disable_replica_allocation`,
in favour for the enable allocation decider which has a single option `allocation.enable` wich can be set to the following values:
`none`, `new_primaries`, `primaries` and `all` (default).
Closes#4488
Simon Willnauer
Suyog Rao
Clinton Gormley
mikemccand
Adrien Grand
Matthew L Daniel
Martijn van Groningen
Lee Hinman