[2.3.x Backport] Use external postgres secret when requested (#8138)

[acohen4]

• use external postgres secret when requested

• skip secret creation if external postgres is set

• handle cloudproxy and tls case for postgres

• generate exactly one postgres secret when both pachd and enterprise-server are enabled

• Revert "generate exactly one postgres secret when both pachd and enterprise-server are enabled"

This reverts commit f088587.

• mutually exclude deployments of pachd and enterprise-server

[codecov]

Codecov Report

Merging #8215 (e291abc) into 2.3.x (d421573) will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            2.3.x    #8215      +/-   ##
==========================================
- Coverage   22.35%   22.25%   -0.10%     
==========================================
  Files         415      415              
  Lines      112192   112192              
==========================================
- Hits        25075    24970     -105     
- Misses      82870    82933      +63     
- Partials     4247     4289      +42     

Impacted Files	Coverage Δ
src/internal/dlock/dlock.go	79.16% <0.00%> (-8.34%)	⬇️
src/internal/dbutil/tx.go	78.57% <0.00%> (-5.72%)	⬇️
src/server/pfs/server/trigger.go	73.21% <0.00%> (-5.36%)	⬇️
src/internal/storage/fileset/postgres_cache.go	85.56% <0.00%> (-4.13%)	⬇️
src/internal/backoff/retry.go	90.90% <0.00%> (-3.64%)	⬇️
src/internal/task/util.go	72.05% <0.00%> (-2.95%)	⬇️
src/server/pfs/server/commit_store.go	79.13% <0.00%> (-2.88%)	⬇️
src/internal/transactionenv/env.go	61.11% <0.00%> (-2.78%)	⬇️
src/internal/collection/postgres_listener.go	77.63% <0.00%> (-2.64%)	⬇️
src/server/pfs/server/master.go	79.48% <0.00%> (-2.57%)	⬇️
... and 14 more

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