Support multiple wal locations for each database

What does this MR do?

We decided to split !66280 (comment 650854524).

In order to add support for idempotent jobs for workers that are using load balancing capabilities, we first need to add support for multiple databases in our sidekiq load balancing middleware.

Support for multiple databases

For the Sidekiq that are using load balancing capabilities, we are currently storing write-ahead log location in job hash

job['database_write_location'] # contains primary write-ahead log location
job['database_replica_location'] # contains replica write-ahead log location in case we schedule a job from replica

In order to support multiple databases, we will update this format and add support for structure that will map correct wal location to corresponding database configuration name:

job['wal_locations'] = {
   main: 'A0/A12FB',
     ci: '0/B12EA'
}

For deduplication, each time when the job gets rejected, we will keep track of the latest wal_location per each database name.

Note: Until we add support for multiple databases to our load balancer, we will use the hardcoded key, only for the main database:

job['wal_locations'] = {
   main: 'A0/A12FB'
}

Since already scheduled jobs could still contain legacy database write location, instead of wal_locations, SidekiqServerMiddlware will support old keys

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?) - Old properties, database_write_location and database_replica_location are contained in structured logs, but AFAIK they are not used in any dashboard, so I don't believe that we need a changelog entry
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #325291 (closed)