Metadata: Update values to strings

[ksierks]

What does this PR do and why?

Converting metadata values to strings, so we can search all metadata values. (See #807.)
Fixes #771.

Screenshots or screen recordings

How to set up and validate locally

Add metadata through the UI:

1. Navigate to a samples page that the logged in user has access to update.
2. Hit the Import Metadata button.
3. Select a file. (See /irida-next-core/test/fixtures/files/metadata/valid.xlsx)
4. Select the Sample ID Column.
5. Hit the Import Metadata button.
6. Verify the sample metadata was added as strings.
7. Follow the Test searching metadata instructions below.

Add metadata through GraphQL:

1. Navigate to http://localhost:3000 and login as admin.
2. Navigate to http://localhost:3000/graphiql.
3. Run the following to retrieve a project:

query getProject{
  project(fullPath: "bacillus/bacillus-anthracis/outbreak-2022") {
    id
    name
    path
  }
}

4. Run the following to create a fresh sample:

mutation createSample{
  createSample(input: { 
    projectId: "<insert here>", 
    name: "Sample Name", 
    description: "Sample Description" 
  }) {
    sample {
      id,
      puid,
      name,
      description
    }
    errors {
      path,
      message
    }
  }
}

5. Run the following to add metadata to the sample:

mutation addMetadataToSample{
  updateSampleMetadata(input: {
    sampleId: "<insert here>", 
    metadata: { true_boolean: true, false_boolean: false, nil: null, empty: "", number: 123, date: "2024-03-11" }
  }) {
    sample{
      id,
      name,
      description,
      metadata
    },
    status,
    errors {
      path
      message
    }
  }
}

6. Verify the date, number, true_boolean, and false_boolean were added successfully as strings.
7. Follow the Test searching metadata instructions below.

Test searching metadata

1. Navigate to a samples page.
2. Toggle metadata.
3. Search using the format FIELD_NAME:FIELD_VALUE.
4. Verify the results when searching for dates, numbers, booleans, etc.

PR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the PR acceptance checklist for this PR.

[github-actions]

Code Metrics Report

Coverage	Test Execution Time
93.3%	8m18s

Code coverage of files in pull request scope (100.0%)

Files	Coverage
app/services/samples/metadata/update_service.rb	100.0%

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Reported by octocov