pgsql: Fix style in a few REPACK ereports

Fix style in a few REPACK ereports

Use consistent "REPACK (CONCURRENTLY)" naming in errhint messages,
matching the actual command syntax and the errmsg text used elsewhere
in the same file. Also improve the ereport() after XLogReadRecord
failure to be like others in the tree.

While at it, remove direct mentions of the DDL in the translatable
strings, both in the same errhint() calls as well as some errmsg()
calls. Add periods where missing.

There are all oversights in 28d534e2ae0a.

Reported-by: Baji Shaik <baji(dot)pgdev(at)gmail(dot)com>
Discussion: https://postgr.es/m/CA+fm-RPxX1xTcYY4qQGPRDXB2-Fy2SDNdZi=zVjr0j=MPg2PaA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3bf63730cb041a834c618082ba3d5e8bf96a31a5

Modified Files
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src/backend/commands/repack.c | 15 ++++++++++-----
src/backend/commands/repack_worker.c | 6 +++++-
src/test/regress/expected/cluster.out | 8 ++++----
3 files changed, 19 insertions(+), 10 deletions(-)