pgsql: doc: Fix confusing description of streaming option in START_REPL

doc: Fix confusing description of streaming option in START_REPLICATION.

Previously, the documentation described the streaming option as a boolean,
which is outdated since it's no longer a boolean as of protocol version 4.
This could confuse users.

This commit updates the description to remove the "boolean" reference and
clearly list the valid values for the streaming option.

Back-patch to v16, where the streaming option changed to a non-boolean.

Author: Euler Taveira <euler(at)eulerto(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/8d21fb98-5c25-4dee-8387-e5a62b01ea7d@app.fastmail.com
Backpatch-through: 16

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e92573917a49ce7d8d0cb5f996813500945616ee

Modified Files
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doc/src/sgml/protocol.sgml | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)