Add full text search to pod logs

What does this MR do?

As per #39166 (closed) and #36342 (closed), adds a search bar to the logs UI.

You need Feature.enable(:enable_cluster_application_elastic_stack)

The search is passed on to ElasticSearch using the simple_query_string function:

The simple_query_string query supports the following operators:

+ signifies AND operation
| signifies OR operation
- negates a single token
" wraps a number of tokens to signify a phrase for searching
* at the end of a term signifies a prefix query
( and ) signify precedence
~N after a word signifies edit distance (fuzziness)
~N after a phrase signifies slop amount

Screenshots

Example of searching for GET in logs, showing disabled behavior when test-instance is selected (doesn't have Elasticsearch)

Screen_Recording_2019-12-12_at_15.33.42

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• 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