Update gitlab-experiment to 0.6.1

What does this MR do?

Updates gitlab-experiment to 0.6.1. Full diff can be found in https://gitlab.com/gitlab-org/gitlab-experiment/-/merge_requests/106.

Changelog:

• Utilize SHA2 and configuration instead of hash strategy - which will go through a deprecation process to keep existing experiments reporting consistently.
• Implements basic percentage of actor rollout - which will likely become the default strategy over time.
• Adds middleware for link visiting / redirection - which is limited to being enabled by a feature flag.

Note:

The 0.6.0 minor version was caused by the SHA2 hashing strategy, since it's not truly backwards compatible. ApplicationExperiment implements its own hashing logic that is backwards compatible (in key_for) which will need to be addressed over time.

0.6.1 has new middleware, which is conditionally enabled in the initializer using a feature flag.

Screenshots (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?)
• 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