pgsql: Add scripts for retrieving the cluster file encryption key

Add scripts for retrieving the cluster file encryption key

Scripts are passphrase, direct, AWS, and two Yubikey ones.

Backpatch-through: master

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d7602afa2ef6d8b2018103dccd89e75b4985ac06

Modified Files
--------------
src/backend/Makefile                         | 12 +++++
src/backend/crypto/ckey_aws.sh.sample        | 50 ++++++++++++++++++
src/backend/crypto/ckey_direct.sh.sample     | 37 ++++++++++++++
src/backend/crypto/ckey_passphrase.sh.sample | 33 ++++++++++++
src/backend/crypto/ckey_piv_nopin.sh.sample  | 63 +++++++++++++++++++++++
src/backend/crypto/ckey_piv_pin.sh.sample    | 76 ++++++++++++++++++++++++++++
src/backend/crypto/ssl_passphrase.sh.sample  | 33 ++++++++++++
7 files changed, 304 insertions(+)