[raft] Compress proposal payloads

[MariemBaccari]

This PR extracts the work of #1587 to compress proposal payloads as a follow-up to #1765 (part of #1709).
Follow-up PRs will implement custom encoding for the payload values which will further reduce the payload size.

A small experiment shows the size difference between the compressed and uncompressed proposals (payloads smaller than 1 kb are not compressed by default):

Case	Cells	Payload (B)	Protobuf uncompressed envelope (B)	Protobuf compressed envelope (B)	Saved
RID delete ISA	-	75	145	145	0.0%
SCD delete OIR	-	213	285	285	0.0%
RID create ISA	1	275	346	346	0.0%
RID create ISA	10	455	526	526	0.0%
RID create ISA	100	2255	2326	1037	55.4%
RID create ISA	1000	20255	20327	7821	61.5%
RID create subscription	1	310	368	368	0.0%
RID create subscription	10	490	548	548	0.0%
RID create subscription	100	2290	2348	1054	55.1%
RID create subscription	1000	20290	20349	7842	61.5%
SCD create subscription	1	384	442	442	0.0%
SCD create subscription	10	564	622	622	0.0%
SCD create subscription	100	2364	2422	1107	54.3%
SCD create subscription	1000	20364	20423	7907	61.3%
SCD create constraint	1	296	361	361	0.0%
SCD create constraint	10	476	541	541	0.0%
SCD create constraint	100	2276	2341	1055	54.9%
SCD create constraint	1000	20276	20342	7845	61.4%
SCD create OIR	1	466	538	538	0.0%
SCD create OIR	10	646	718	718	0.0%
SCD create OIR	100	2446	2518	1154	54.2%
SCD create OIR	1000	20446	20519	7962	61.2%