Upgrade Spring Dependences & HAL Browser

[tdonohue]

References

• Fixes https://github.com/DSpace/DSpace/security/dependabot/8

Description

• Upgrade us to the latest version of Spring dependencies. This requires some minor code refactors to align with latest Spring code. This PR updates us to these versions:
  • Spring 5.3.16
  • Spring Boot 2.6.4
  • Spring Security 5.6.2
• Migrate to installing HAL Browser via WebJARs (as it's no longer included in Spring Data REST)
  • Updated Hal Browser to use Bootstrap 4, based heavily on Updated Bootstrap mikekelly/hal-browser#102. This required code HTML & CSS changes to the HAL Browser
  • Updated HAL Browser dependencies / vendor libraries, by switching them to use latest version available via WebJar.
  • NOTE: These HAL Browser updates were minor, but should allow us to remain on HAL Browser until HAL Explorer becomes more widely used, see Investigate switching from HAL Browser to HAL Explorer for REST API #3017
• Also upgraded to latest version of Solr (version 8.9.0) which doesn't cause SWORDv2 to break (see Swordapp's SWORDv2 Java Library is unmaintained & uses outdated/obsolete libraries  #8188)

NOTE: This PR has a few IT cleanup commits which overlap with PR #8195, as these changes were necessary in both these PRs to get all tests to pass. After one PR is merged though, I'll rebase the other.

Instructions for Reviewers

• Review/scan code changes
• More importantly, install this PR & try out the HAL Browser at http://localhost:8080/server/
  • Make sure all normal actions work properly. Browse around, try login & logout, etc.
  • You may notices some minor differences in style/CSS after the upgrade to Bootstrap 4, but all buttons, etc should work fine.

[tdonohue]

NOTE FOR REVIEWERS: This PR passes all required tests despite the red (❌ ). It seems to be failing a Snyk check simply because it cannot access the Snyk account anymore. Unfortunately, I don't see any way to remove that Snyk check from this PR other than by recreating the PR entirely. I have however removed this Snyk check from future PRs, as it seems like something changed in Snyk recently that causes it to be less stable for PR checks.

[tdonohue]

Close & reopen to re-run tests & see if it triggers GitHub to remove the misleading red ❌ .

[tdonohue]

Close & reopen to re-run tests & see if it triggers GitHub to remove the misleading red ❌ .

[tdonohue]

Closing this PR in favor of #8215 (which is a recreation of this same PR). GitHub has somehow messed up this PR...the comments above are duplicating, etc. Might be a temporary issue, but recreated the PR just in case.