fix(relayer): update relayer flag env var name

[cyberhorsey]

also add a mutex on subscription so we dont get multiple block errors being saved when multiple bridges are located in the same block.

[vercel]

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Name	Status	Preview	Updated (UTC)
bridge-ui-v2-a6	✅ Ready (Inspect)	Visit Preview	Jan 31, 2024 8:19pm

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (5fa1331) 27.36% compared to head (f4e8ed8) 27.05%.

Files	Patch %	Lines
packages/relayer/indexer/indexer.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           alpha-6   #15622      +/-   ##
===========================================
- Coverage    27.36%   27.05%   -0.32%     
===========================================
  Files           99      102       +3     
  Lines         5795     6084     +289     
===========================================
+ Hits          1586     1646      +60     
- Misses        4041     4258     +217     
- Partials       168      180      +12     

Flag	Coverage Δ		*Carryforward flag
eventindexer	17.28% <ø> (ø)		Carriedforward from c9dbeae
guardian-prover-health-check	36.13% <ø> (ø)		Carriedforward from c9dbeae
relayer	38.03% <66.66%> (-2.55%)	⬇️

*This pull request uses carry forward flags. Click here to find out more.

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