Add Readpool index

[Sriep]

Fixes

Add index to readpool

Changes

Need to be mentioned in CHANGELOG.md?

Tests

Tasks to complete before merging PR:

• Ensure system tests are passing. If not Run them manually to check for any regressions 📋
• Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• Merge your system tests PR to master AFTER merging this PR

Associated PRs (Link as appropriate):

• blobber:
• gosdk:
• system_test:
• zboxcli:
• zwalletcli:
• Other: ...

[service-0chain]

Manual system tests [failure] with the following config

config	value
tests skipped	false
system-tests
gosdk	NOT OVERRIDDEN
zboxcli
zwalletcli
0chain	readpool_pk
blobber
authorizer
0box
0dns

[service-0chain]

Manual system tests [success] with the following config

config	value
tests skipped	false
system-tests
gosdk	NOT OVERRIDDEN
zboxcli
zwalletcli
0chain	readpool_pk
blobber
authorizer
0box
0dns

[dabasov]

lgtm

[codecov-commenter]

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@@               Coverage Diff                @@
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  Hits                     ?    18589           
  Misses                   ?    43765           
  Partials                 ?     2198           

Flag	Coverage Δ
Unit-Tests	28.79% <0.00%> (?)

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