ERM-3759: Add missing primary keys in web toolkit

[mchaib-k-int]

We noticed these tables (listed below) from web-toolkit were missing primary keys when investigating mod-agreements.

To test this PR works I:

• Ran ./gradlew clean and ./gradlew publishToMavenLocal on the main branches of web-toolkit-ce and grails-okapi locally.
• Uncommented mavenLocal()'s in the build.gradle of mod-agreements (on main) and updated the web-toolkit version to match the inferred version bump from publishMavenToLocal.
• Ran mod-agreements and dropped tenant. Checked which tables were missing primary keys in PgAdmin (it was the tables in list below).
• Made a new branch for this PR with the changes to web-toolkit-ce: Add primary keys in the src/migrations/wtk/multi-value-custprops.feat.groovy migartion file.
• Switched to the branch and ran ./gradlew clean and ./gradlew publishToMavenLocal.
• Stopped the mod-agreements application and ran ./gradlew clean on mod-agreements.
• Restarted mod-agreements and then ran the trigger-migrations.sh script.
• Checked on PgAdmin that all the custom_property tables now have primary keys.

Tables with new primary keys added:
"custom_property_multi_blob_value"
"custom_property_multi_decimal_value"
"custom_property_multi_integer_value"
"custom_property_multi_local_date_value"
"custom_property_multi_refdata_refdata_value"
"custom_property_multi_text_value"