Make fingerprint nullable for group_deploy_keys table

What does this MR do and why?

Contributes to #360149 (closed)

Problem

FIPS does not support MD5 algorithm. We want to deprecate MD5 fingerprints in the future. Table group_deploy_keys was created from keys (see MR: !30886 (merged)). But there is a difference group_deploy_keys require MD5 fingerprint presence but keys table does not.

Solution

Make fingerprint field from group_deploy_keys to support NULL values. It will simplify MD5 deprecation process.

Database

== 20220421114418 MakeFingerprintNullableForGroupDeployKey: migrating =========
-- change_column_null(:group_deploy_keys, :fingerprint, true)
   -> 0.0043s
== 20220421114418 MakeFingerprintNullableForGroupDeployKey: migrated (0.0044s)

== 20220421114418 MakeFingerprintNullableForGroupDeployKey: reverting =========
== 20220421114418 MakeFingerprintNullableForGroupDeployKey: reverted (0.0000s)

MR acceptance checklist

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