Add UpdateRole rpc and an expired flag to Invitations

[rdimitrov]

Summary

The following PR:

• adds an UpdateRole RPC method
• adds an expired flag to the Invitations message

Related to: https://github.com/stacklok/epics/issues/212

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Outline how the changes were tested, including steps to reproduce and any relevant configurations.
Attach screenshots if helpful.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 53.352% (-0.02%) from 53.367%
when pulling 945e699 on proto
into 5d1bd36 on main.

[coveralls]

coverage: 53.362% (-0.005%) from 53.367%
when pulling 8399020 on proto
into 5d1bd36 on main.

[evankanderson]

As mentioned offline, the expired boolean makes sense because the client time and server time may differ.

[coveralls]

coverage: 53.464% (+0.01%) from 53.454%
when pulling 6de0ef4 on proto
into 266f0f4 on main.

[coveralls]

coverage: 53.445% (-0.005%) from 53.45%
when pulling f38f862 on proto
into cd5d5b4 on main.

[coveralls]

coverage: 53.422% (+0.005%) from 53.417%
when pulling 5530d51 on proto
into 5d33ee6 on main.

[coveralls]

coverage: 53.39% (-0.01%) from 53.4%
when pulling b14cf47 on proto
into cd7a0f2 on main.

[coveralls]

coverage: 53.39%. remained the same
when pulling db5cd05 on proto
into f0a5d42 on main.

[coveralls]

coverage: 53.39% (-0.005%) from 53.395%
when pulling 5c285c1 on proto
into 20581f6 on main.