tenable_sc.vulnerability: Update mapping of tenable_sc.vulnerability.plugin.text field to match_only_text

[kcreddy]

Proposed commit message

The "tenable_sc.vulnerability.plugin.text" field stores several 
details of vulnerable packages found on the host. It is currently 
mapped to "keyword". It can grow larger than maximum "ignore_above" 
limit of keywordfields, making it unusable in searches.

This PR updates the data type of "tenable_sc.vulnerability.plugin.text" 
field to "match_only_text" to allow searches on this field.

This is a breaking-change because the data types "keyword" and 
"match_only_text" are from different family [1] and could break 
users' custom Kibana dashboards or queries.

[1] https://www.elastic.co/docs/reference/elasticsearch/mapping-reference/field-data-types

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Screenshots

Before

After

[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 229131e

cc @kcreddy

[elastic-vault-github-plugin-prod]

Package tenable_sc - 2.0.0 containing this change is available at https://epr.elastic.co/package/tenable_sc/2.0.0/