sql-parser: align SUBSCRIBE syntax with CREATE SINK/SELECT

[benesch]

The "output options" for SUBSCRIBE (i.e., the ENVELOPE and WITHIN TIMESTAMP ORDER BY clauses) were jammed in at the end of the statement, as in:

SUBSCRIBE t WITH (SNAPSHOT) AS OF 1 UP TO 2 ENVELOPE UPSERT KEY (a)

This was inconsistent with our other SQL statements. In particular, CREATE SOURCE and CREATE SINK always put the WITH options at the very end of the statement:

CREATE SINK ... WITH (SNAPSHOT)

And SELECT always puts the AS OF clause at the very end of the statement:

SELECT * FROM t WHERE ... AS OF 1

This commit restores the consistency that used to be present in SUBSCRIBE by moving the output options to before the AS OF, UP TO, and WITH options:

SUBSCRIBE t ENVELOPE UPSERT KEY (a) WITH (SNAPSHOT) AS OF 1 UP TO 2

The old syntax remains supported for backwards compatibility, but is softly deprecated. Only the new syntax will be mentioned in the docs going forward.

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Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
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• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.