ISD-2184 Implement reverseproxy relation

[Thanhphan1147]

Implement support for the reverseproxy:http relation. As we prioritize having feature parity with the legacy haproxy charm as well as for the new charm to be a drop-in replacement, part of the code of the legacy charm is added and isolated in the legacy.py module (all lint checks disabled).

Supported workflow:

juju deploy pollen
juju deploy ./haproxy_amd64.charm
juju relate pollen haproxy
curl <haproxy_unit_ip>

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)

[cbartz]

LGTM, minor comments. I am missing unit tests for the changes. @Thanhphan1147

[github-actions]

Test coverage for 1f0ad38

Name                      Stmts   Miss Branch BrPart  Cover   Missing
---------------------------------------------------------------------
src/charm.py                 92     43     12      0    47%   80-81, 86-87, 92, 101-103, 112-115, 126-133, 140-141, 149-162, 166, 170, 174-176, 180-195
src/haproxy.py               47     10      2      1    78%   64, 73-74, 91-100, 110-112
src/http_interface.py        65     23      4      0    61%   73, 82, 91, 96, 105-107, 125, 137, 149, 161, 169-174, 189-199
src/state/config.py          40     22      6      0    39%   50-70, 85-93, 105-106
src/state/tls.py             38     12      6      1    61%   55-68, 91-96
src/state/validation.py      31     17      6      0    38%   59-75
src/tls_relation.py         117      2     18      1    96%   254-255, 263->266
---------------------------------------------------------------------
TOTAL                       430    129     54      3    66%

Static code analysis report

Run started:2024-10-16 12:14:44.254414

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1869
  Total lines skipped (#nosec): 1
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 3

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):

[Thanhphan1147]

@cbartz can I ask you to take a look at the PR again and leave your reviews? I'll add the unit tests in a follow-up PR.

Thanks!